Merge branch 'develop' of https://github.com/llnl/spack into develop

lib/spack/docs/basic_usage.rst

lib/spack/docs/configuration.rst

lib/spack/docs/features.rst

lib/spack/docs/packaging_guide.rst

lib/spack/spack/cmd/find.py

lib/spack/spack/test/__init__.py

lib/spack/spack/test/cmd/find.py

var/spack/repos/builtin/packages/openmpi/package.py

var/spack/repos/builtin/packages/stream/package.py