packaging: engine-backup: align db creation instructions with dwh

Replace 'create user' with 'create role'.

Also add a missing quote.

Change-Id: Id11a2746ced31a2731a8f8d76a29b3ea4b6a5478
Bug-Url: https://bugzilla.redhat.com/1040572
Signed-off-by: Yedidyah Bar David <didi@redhat.com>