Fixes for various hash issues (#2626)

* Better output for disambiguate_specs()

* Fix wrong exception name.

* Fix satsifies(): concrete specs require matching by hash.

- Fixes uninstall by hash and other places where we need to match a
  specific spec.

- Fix an error in provider_index (satisfies() call was backwards)

- Fix an error in satisfies_dependencies(): checks were too shallow.

* Fix default args in Spec.tree()

* Move installed_dependents() to DB to avoid unknown package error.

* Make `spack find` and `sapck.store.db.query()` faster for hashes.

* Add a test to ensure satisfies() respects concrete Specs' hashes.