packaging: Fix problems in engine-backup.sh

Backup more files.

Change SCOPE's dbonly to db everywhere.

Do not fail if some files are missing (e.g.
/etc/firewalld/services/ovirt-postgres.xml is not
always created by setup).

Fix selinux contexts on restore.

Refuse to restore if engine service is running.

Bug-Url: https://bugzilla.redhat.com/1020277
Change-Id: I464e795627af23712696212e4589e4b8480bb8a0
Signed-off-by: Yedidyah Bar David <didi@redhat.com>