Group creation: Add msSFU30Name only when --nis-domain was given

Group creation: Add msSFU30Name only when --nis-domain was given

This fixes a bug, that all new created groups automatically get an
msSFU30Name attribute added. This should only be the case, when
we also have a nis-domain (samba-tool --nis-domain=...).

Bugreport: https://bugzilla.samba.org/show_bug.cgi?id=11315

Signed-off-by: Marc Muehlfeld <mmuehlfeld@samba.org>
Reviewed-by: Christian Ambach <ambi@samba.org>
Autobuild-User(master): Christian Ambach <ambi@samba.org>
Autobuild-Date(master): Tue Jun 16 11:58:02 CEST 2015 on sn-devel-104