Filter out alembic logs below WARNING in tests
Filter out alembic logs below WARNING in tests

During functional tests we see quite a bit of alembic
INFO level logging which we don't really need. This
change sets the alembic logging level to WARNING to
remove that noise.

Change-Id: I9550e1c0c93b48e234f429204e27960d0d1cda81
Related-Bug: #1813147

klmitch/nova,klmitch/nova,rahulunair/nova,mahak/nova,klmitch/nova,openstack/nova,mahak/nova,klmitch/nova,rahulunair/nova,mahak/nova,rahulunair/nova,openstack/nova,openstack/nova