webadmin: Sort checkbox columns in Network/Clusters subtab

Implemented sorting using the recently added default sorting behavior
in CheckboxColumn.

Change-Id: Ic1ea118ded65ce1ebe426a7bfbf2a7cc993380b0
Bug-Url: https://bugzilla.redhat.com/1120054
Signed-off-by: Lior Vernia <lvernia@redhat.com>