webadmin: Fixed behavior of "Required All" column header

It previously behaved as if required was identical to assigned, thus
not affecting whether the network was required in the cluster from
which the dialog was opened. Now it behaves as expected.

Change-Id: I05fd73f64f2bbc38ce1b7bc4cf494d0cf1442f00
Bug-Url: https://bugzilla.redhat.com/1014661
Signed-off-by: Lior Vernia <lvernia@redhat.com>