frontend: Clear Inactive ISO Domain Images List

When an ISO domain is not active, navigating to its images subtab
should not query for the images, but show an empty list.

Change-Id: Idb29eb14a07a8084b62bda5ac41769ce964bac16
Bug-Url: https://bugzilla.redhat.com/1155191
Signed-off-by: Idan Shaby <ishaby@redhat.com>