Suspend single and multi threaded engines

Change-Id: I908c8f4e98f715a4c4b5b6fa7db35e125439ec38
Merge "Suspend single and multi threaded engines"
Create database from models for SQLite

Alembic does not support SQLite, and we don't recommend to use SQLite
in production deployments, so migrations are rarely needed for SQLite.
So we don't bother about working around SQLite limitations, and create
database from models when it is in use. Of course, we still use
alembic to migrate schema on 'real' databases.

Change-Id: I8237a29c7bf5b60136bb1b72fd029fe9ce1abe1f