The perl binary can also be called `perlX.Y.Z` if using a development
build or simply using the versioned binary.

We were also dropping all sbang arguments, since `exec $interpreter_v`
was only using the first element of the `interpreter_v` array.

Rework Spack's continuous integration workflow to be environment-based.

- Add the `spack ci` command, which replaces the many scripts in `bin/`

- `spack ci` decouples the CI workflow from the spack instance:
  - CI is defined in a spack environment
  - environment is in its own (single) git repository, separate from Spack
  - spack instance used to run the pipeline is up to the user
  - A new `gitlab-ci` section in environments allows users to configure how
    specs in the environment should be mapped to runners
  - Compilers can be bootstrapped in the new pipeline workflow

- Add extensive documentation on pipelines (see `pipelines.rst` for further details)
- Add extensive tests for pipeline code

This extends Spack functionality so that it can fetch sources and binaries from-, push sources and binaries to-, and index the contents of- mirrors hosted on an S3 bucket.

High level to-do list:

- [x] Extend mirrors configuration to add support for `file://`, and `s3://` URLs.
- [x] Ensure all fetching, pushing, and indexing operations work for `file://` URLs.
- [x] Implement S3 source fetching
- [x] Implement S3 binary mirror indexing
- [x] Implement S3 binary package fetching
- [x] Implement S3 source pushing
- [x] Implement S3 binary package pushing

Important details:

* refactor URL handling to handle S3 URLs and mirror URLs more gracefully.
  - updated parse() to accept already-parsed URL objects.  an equivalent object
    is returned with any extra s3-related attributes intact.  Objects created with
    urllib can also be passed, and the additional s3 handling logic will still be applied.

* update mirror schema/parsing (mirror can have separate fetch/push URLs)
* implement s3_fetch_strategy/several utility changes
* provide more feature-complete S3 fetching
* update buildcache create command to support S3

* Move the core logic for reading data from S3 out of the s3 fetch strategy and into
  the s3 URL handler.  The s3 fetch strategy now calls into `read_from_url()` Since
  read_from_url can now handle S3 URLs, the S3 fetch strategy is redundant.  It's
  not clear whether the ideal design is to have S3 fetching functionality in a fetch
  strategy, directly implemented in read_from_url, or both.

* expanded what can be passed to `spack buildcache` via the -d flag: In addition
  to a directory on the local filesystem, the name of a configured mirror can be
  passed, or a push URL can be passed directly.

The Python landscape is going to be changing in 2020, and Python 2 will
be end of life. Spack should *prefer* Python 3 to Python 2 by default,
but we still need to run on systems that only have Python2 available.

This is trickier than it sounds, as on some systems, the `python` command
is `python2`; on others it's `python3`, and RHEL8 doesn't even have the
`python` command.  Instead, it makes you choose `python3` or
`python2`. You can thus no longer make a simple shebang to handle all the
cases.

This commit makes the `spack` script bilingual.  It is still valid
Python, but its shebang is `#!/bin/sh`, and it has a tiny bit of shell
code at the beginning to pick the right python and execute itself with
what it finds.

This has a lot of advantages.  I think this will help ensure that Spack
works well in Python3 -- there are cases where we've missed things
because Python2 is still the default `python` on most systems.  Also,
with this change, you do not lose the ability to execute the `spack`
script directly with a python interpreter.  This is useful for forcing
your own version of python, running coverage tools, and running profiling
tools.  i.e., these will not break with this change:

```console
$ python2 $(which spack) <args>
$ coverage run $(which spack) <args>
$ pyinstrument $(which spack) <args>
```

These would not work if we split `spack` into a python file and a shell
script (see #11783).  So, this gives us the best of both worlds.  We get
to control our interpreter *and* remain a mostly pure python executable.

- improve mirror git repo management
- minio s3 implementation needs endpoint_url
- Remove image key from rebuild-index job
- Remove image, rely on tags instead

- Delete references to ruamel.yaml at Spack start-up, if they are present

- ruamel.yaml generates a .pth file when installed via pip that has the
  effect of always preferring the version of this package installed at
  site scope (effectively preventing us from vendoring it).

- This mechanism triggers when implicitly importing the 'site' module
  when the python interpreter is started. In this PR we explicitly delete
  references to 'ruamel.yaml' and 'ruamel' in sys.modules, if any, after
  we set 'sys.path' to search from the directory where we store vendored
  packages. This ensures that the imports after those statements will be
  done from our vendored version.

- See #9206 for further details

- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
  - core and most packages are (Apache-2.0 OR MIT)
  - a very small number of remaining packages are LGPL-2.1-only

- ruamel.yaml allows round-tripping comments from/to files
- ruamel.yaml is single-source, python2/python3 compatible

* update help of `clean --all` to include `-p`
* remove old orphaned `.pyc` removal
* restrict removal or orphaned pyc files to `lib/spack` and `var/spack`

* Vendor ordereddict for python2.6 only

This commit substitutes the custom module 'ordereddict_backport' with
the more known 'ordereddict' and vendors it only for python 2.6. Other
supported versions of python will use 'collections.OrderedDict'.

* Use absolute imports also for python 2.6

See PEP-328 for more information on the subject

* Added provenance of vendored ordereddict

We moved to a new GitHub org! Now make the code and docs reflect that.

This adds sbang hook support for node-js and fixes the sbang filter
for lua (the character class exclusion was swallowing newlines and
reporting a false positive if lua was mentioned anywhere in the 
file).

* fix intltool_sbang issue #4191

* add per dep even if already depending on perl-xml-parser

* adding more comment, properly spaced

- Full help is now only generated lazily, when needed.
  - Executing specific commands doesn't require loading all of them.
  - All commands are only loaded if we need them for help.

- There is now short and long help:
  - short help (spack help) shows only basic spack options
  - long help (spack help -a) shows all spack options
  - Both divide help on commands into high-level sections

- Commands now specify attributes from which help is auto-generated:
  - description: used in help to describe the command.
  - section: help section
  - level: short or long

- Clean up command descriptions

- Add a `spack docs` command to open full documentation
  in the browser.

- move `spack doc` command to `spack pydoc` for clarity

- Add a `spack --spec` command to show documentation on 
  the spec syntax.

* spack: no stacktrace if not in debug mode + fix emacs variant

* emacs: removed dead code

- Add -P <STAT> argument so that caller can specify a sort column for
  cProfile. Can specify multiple columns with commas. e.g.:
      spack -P cumtime,module

- Add --lines option to Spack spec to control number of profile lines
  displayed

- Sort by time by default (because it works in all Python versions)

- Show sort column options in command help.

- Do a short profile run in the unit tests.

- Update version guard in spack script to allow python 3
- Update min required version in the docs

- convert print, StringIO, except as, octals, izip
- convert print statement to print function
- convert StringIO to six.StringIO
  - remove usage of csv reader in Spec, in favor of simple regex
  - csv reader only does byte strings
- convert 0755 octal literals to 0o755
- convert `except Foo, e` to `except Foo as e`
- fix a few places `str` is used.
  - may need to switch everything to str later.
- convert iteritems usages to use six.iteritems
- fix urllib and HTMLParser
- port metaclasses to use six.with_metaclass
- More octal literal conversions for Python 2/3
- Fix a new octal literal.
- Convert `basestring` to `six.string_types`
- Convert xrange -> range
- Fix various issues with encoding, iteritems, and Python3 semantics.
- Convert contextlib.nested to explicitly nexted context managers.
- Convert use of filter() to list comprehensions.
- Replace reduce() with list comprehensions.
-  Clean up composite: replace inspect.ismethod() with callable()
- Python 3 doesn't have "method" objects; inspect.ismethod returns False.
- Need to use callable in Composite to make it work.
- Update colify to use future division.
- Fix zip() usages that need to be lists.
- Python3: Use line-buffered logging instead of unbuffered.
- Python3 raises an error with unbuffered I/O
  - See https://bugs.python.org/issue17404

- Update YAML version to support Python 3
- Python 3 support for ordereddict backport
- Exclude Python3 YAML from version tests.
- Vendor six into Spack.
- Make Python version-check tests work with Python 3
- Add ability to add version check exceptions with '# nopyqver' line
  comments.

- Remove stale reference to `import nose` from `bin/spack` script.
- Add `py` to externals (missing dependency for `pytest`)

* Porting: substitute nose with ytest

This huge commit substitutes nose with pytest as a testing system. Things done here:

* deleted external/nose as it is no longer used
* moved mock resources in their own directory 'test/mock/'
* ported two tests (cmd/find, build_system) to pytest native syntax as an example
* build_environment, log: used monkeypatch instead of try/catch
* moved global mocking of fetch_cache to an auto-used fixture
* moved global mocking from test/__init__.py to conftest.py
* made `spack test` a wrapper around pytest
* run-unit-tests: avoid running python 2.6 tests under coverage to speed them up
* use `pytest --cov` instead of coverage run to cut down testing time

* mock/packages_test: moved mock yaml configuration to files instead of leaving it in the code as string literals

* concretize.py: ported tests to native pytest, reverted multiprocessing in pytest.ini as it was creating the wrong report for coveralls

* conftest.py, fixtures: added docstrings

* concretize_preferences.py: uses fixtures instead of subclassing MockPackagesTest

* directory_layout.py: uses fixtures instead of subclassing MockPackagesTest

* install.py: uses fixtures instead of subclassing MockPackagesTest

* optional_deps.py: uses fixtures instead of subclassing MockPackagesTest

optional_deps.py: uses fixtures instead of subclassing MockPackagesTest

* packages.py: uses fixtures instead of subclassing MockPackagesTest

* provider_index.py: uses fixtures instead of subclassing MockPackagesTest

* spec_yaml.py: uses fixtures instead of subclassing MockPackagesTest

* multimethod.py: uses fixtures instead of subclassing MockPackagesTest

* install.py: now uses mock_archive_url

* git_fetch.py: uses fixtures instead of subclassing MockPackagesTest

* hg_fetch.py: uses fixtures instead of subclassing MockPackagesTest

* svn_fetch.py, mirror.py: uses fixtures instead of subclassing MockPackagesTest
repo.py: deleted

* test_compiler_cmd.py: uses fixtures instead of subclassing MockPackagesTest

* cmd/module.py, cmd/uninstall.py: uses fixtures instead of subclassing MockDatabase

* database.py: uses fixtures instead of subclassing MockDatabase, removed mock/database

* pytest: uncluttering fixture implementations

* database: changing the scope to 'module'

* config.py: uses fixtures instead of subclassing MockPackagesTest

* spec_dag.py, spec_semantics.py: uses fixtures instead of subclassing MockPackagesTest

* stage.py: uses fixtures instead of subclassing MockPackagesTest. Removed mock directory

* pytest: added docstrings to all the fixtures

* pytest: final cleanup

* build_system_guess.py: fixed naming and docstrings as suggested by @scheibelp

* spec_syntax.py: added expected failure on parsing multiple specs closes #1976

* Add pytest and pytest-cov to Spack externals.

* Make `spack flake8` ignore externals.

* run-unit-tests runs spack test and not pytest.

* Remove all the special stuff for `spack test`

- Remove `conftest.py` magic and all the special case stuff in `bin/spack`

- Spack commands can optionally take unknown arguments, if they want to
  handle them.

- `spack test` is now a command like the others.

- `spack test` now just delegates its arguments to `pytest`, but it does
  it by receiving unknown arguments and NOT taking an explicit
  help argument.

* Fix error in fixtures.

* Improve `spack test` command a bit.

- Now supports an approximation of the old simple interface
- Also supports full pytest options if you want them.

* Use external coverage instead of pytest-cov

* Make coverage use parallel-mode.

* change __init__.py docs to include pytest

* Use JSON for the database instead of YAML.

- JSON is much faster than YAML *and* can preserve ordered keys.
  - 170x+ faster than Python YAML when using unordered dicts
  - 55x faster than Python YAML (both using OrderedDicts)
  - 8x faster than C YAML (with OrderedDicts)

- JSON is built into Python, unlike C YAML, so doesn't add a dependency.
- Don't need human readability for the package database.
- JSON requires no major changes to the code -- same object model as YAML.
- add to_json, from_json methods to spec.

* Add tests to ensure JSON and YAML don't need to be ordered in DB.

* Write index.json first time it's not found instead of requiring reindex.

* flake8 bug.

The option -s now causes file and line number information to be printed
along with any invocation of msg, info, etc...

This will greatly ease debugging.

- generalized and fixed to work with any key in YAML file
- simplified schema writing, as well
- add more unit tests for the config system
- Rename test/yaml.py to test/spack_yaml.py
  - Add test/yaml.pyc to ignored pyc files.