Sync db.models and migrations.

This patch syncs models with migrations for:
- DNSDomain
- AggregateMetadata
- BandwidthUsage

Blueprint: db-sync-models-with-migrations

Change-Id: I09c48bac5ed780a7ec1b89cc8ce0684f4903d9dd
Fix types in test_ec2_ids_not_found_are_printable

This test fails on PostgreSQL when trying to compare
the VolumeIdMapping.id column (Integer) with a passed
string value.

Blueprint: db-api-tests-on-all-backends

Change-Id: Ie529d25029667a5279f9c70f0f3f081b87fb6acb
Merge "Fix types in test_ec2_ids_not_found_are_printable"
Merge "Sync db.models and migrations."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp