packaging: setup: Do not create a new db on upgrade

Before this change, the following scenario made engine-setup emit
a warning and create a new db:
1. engine-setup
2. service ovirt-engine stop; service postgresql stop
3. engine-setup

This change changes the warning to an error (exception) unless
it's during cleanup.

Bug-Url: https://bugzilla.redhat.com/1014012
Change-Id: Ia336e951860f6e1a6a829cabf5e6b5e10592089b
Signed-off-by: Yedidyah Bar David <didi@redhat.com>