Pin jsonschema version below 1.0.0.

The latest jsonschema version breaks the unit tests. This commit pins
the version to be less than the latest release.

Fixes bug 1132840

Change-Id: Ib4db4782f995cee179445ca11d2b6a7f13a6b457
Fix migration 016 for sqlite.

Sqlite doesn't support dropping a column from a table. The
downgrade path for migration 016 performed this. So this commit adds the
sql file to perform the downgrade manually.

Change-Id: I6aae263c3aab03a383c47fd29c46f0cc9b857549
Refactor data migration tests

This commit adds a more general framework for testing data
transitions at any db migration. Based on the test migration
framework in nova.

This commit also updates the existing individual migration
tests to use the new framework.

Change-Id: I917cfefe266a98f6c63613ac071af2dd676d67a1