Fix StorageDomainDoesNotExist raise messages.

Change-Id: I8ab8cb6050090f4eb7efdcff0bef77f694c6c191
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/14008
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Tested-by: Daniel Paikov <paikov@gmail.com>