packaging: setup: better handling of preexisting storage domain

Better handling of preexisting storage domain validating it

Change-Id: I622e0540ca21eea5ebddbfa4361bfb6537ca42d8
Bug-Url: https://bugzilla.redhat.com/1155637
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>