Add migration tests with data

This commit adds a test class based on the glance test_migrations code
and using some of the code from the WIP oslo.db alembic migration test
mixin.[1] This framework will run the migrations against a real db and
using _pre_upgrade*, _post_upgrade*, and _check* methods data can be
injected and validated during migrations.

[1] https://review.openstack.org/99965

Change-Id: Idb8f203e9e0c721cc3459af2aa75d3c0b20b48fa
Merge "Add migration tests with data"