packaging: setup: added a test on postgres status

This new implementation adds an actual test with the
postgres server to verify it responds to sql queries.

It covers for cases where the postgresql service reports
status up but the server is not ready to receive connections.
In such cases the setup fails on DB operations.

Change-Id: I1907f0f5a7f20225128a875e2a84c5e8de11e6c3
Bug-Url: https://bugzilla.redhat.com/1029969
Signed-off-by: Alex Lourie <alourie@redhat.com>