webadmin: Don't trigger event when assigning label

Since we're only mocking another operation to assign a label to a NIC,
the code is changed to not trigger an event (that would affect the
status panel).

Change-Id: I676ddff5293d1a7e22a911bb3b03e6da6707c493
Bug-Url: https://bugzilla.redhat.com/1115109
Signed-off-by: Lior Vernia <lvernia@redhat.com>