packaging: setup - do not accept non-alphanumeric iso domain name

ISO Domain name must contian only alphanumeric characters.

Change-Id: If4caf14c80ebbabef6d565b832e725c7cf88c27c
Bug-Url: https://bugzilla.redhat.com/1064373
Signed-off-by: Ofer Schreiber <oschreib@redhat.com>