Run tempest-dsvm-postgres-full with nova-api-metadata binary

We want to make sure nova supports runing nova-api-metadata as a
separate binary, so run postgres test in this mode.

devstack-gate patch: Iddd44f7ee43b9287a788dea49eaa484316f8da04

Change-Id: Id7169e9ec72a934c2c2116f6e6156419b51b104f
Related-Bug: #1270845
Merge "Run tempest-dsvm-postgres-full with nova-api-metadata binary"