packaging: setup: legacy: use postgres db user

Take db user from /etc/sysconfig/ovirt-engine and its credentials
from pgpass.

Bug-Url: https://bugzilla.redhat.com/1049654
Change-Id: I391cc532fd1673db9f6adb29fc0cce052992fda4
Signed-off-by: Yedidyah Bar David <didi@redhat.com>