Add missing tests for db.instance_type_* methods

There was no tests in test_db_api for instance_type_* methods.

Add tests to ensure that all works.
Also these tests allow us to refactor work with session and
to add missing unique constraints.

Fix bug in instance_type_get_all, we shouldn't remove
is_public from input filters dictionary.

blueprint db-api-tests

Change-Id: Ia02d73e6ffd964d6edb605039eb95e9f90ff0482
Bring back colorizer again with error results.

This was actually a pretty simple fix. When I switched the base
test result class to testtools I lost the methods that were
printing out the errors at the end. This adds the (colorized!)
methods so errors print successfully.

fixes bug 1159116

Change-Id: Ib09d7e18ddf27015ff735a30137421d865382359
Merge "Bring back colorizer again with error results."
Merge "Add missing tests for db.instance_type_* methods"