core: When ISO domain is attached to multiple DCs it appears multiple times

In the storage main tab, when an ISO domain is attached to multipe data
center, it appears in the list one time for each data centers

Change-Id: I0b874fc33c660af29c2e20a15898444db12f6f6b
Signed-off-by: Tal Nisan <tnisan@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1150525