Previously when we had one repo with one alembic branch we would
create a milestone revision on that single branch. Now we have
multiple repos and expand/contract branches for each repo. So
now we tag the final revision on every branch when we make a
milestone release.
The database can be upgraded with the command:
neutron-db-manage upgrade <milestone>
where <milestone> is an alias for all the revisions for a
milestone.
Closes-Bug: #1559318
Change-Id: Ie1324f8f998e1d551fc0aa3e3bc5f6a51523365a
e2971f49f0