turn on non-voting postgresql tempest

this turns on non-voting postgresql for the core projects.

This enables us to track and handle pg issues showing up in projects
with the goal of actually gating on pg by the time we get to g-3.

Change-Id: I163e818978823a8ac6ee9016892e1d5824202493
Reviewed-on: https://review.openstack.org/20780
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins