webadmin: DirectLUN iSCSI - fix radio-buttons behavior

Fixed radio-button single-selection behavior for iSCSI DirectLUN
(added single-selection listeners for LUNs that
are ordered by Target as well).

Change-Id: I5ecb21cc817d0383fbdc7d6bdc955e6a1c38af04
Bug-Url: https://bugzilla.redhat.com/918568
Signed-off-by: Daniel Erez <derez@redhat.com>