Fix ReservationTestCase on PostgreSQL

setUp() of ReservationTestCase calls quota_reserve() passing
timeutils.utcnow() as a value of 'until_refresh' argument.
until_refresh column is actually of type int rather than
datetime or varchar, so these tests fail on PostgreSQL.

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

Change-Id: Ib57579db2080f44bd41b91e83b0eee6f77f51840
Merge "Fix ReservationTestCase on PostgreSQL"