packaging: setup: use db creds from env if not None

Fixes Icac431a840c1207313c5a4b6e47eace93d1dd099 - without this
engine-cleanup fails.

Change-Id: Ib0c55faeb8ffef8823b29016617aa56d2f54ae9c
Related-To: https://bugzilla.redhat.com/1094016
Signed-off-by: Yedidyah Bar David <didi@redhat.com>