webadmin: Disable buttons on ghost entry

A relatively recent refactoring/enhancement caused a small regression
in several widgets, this is now fixed by calling superclass
implementation of toggleGhost() (or not overriding it to do
nothing). That patch wasn't pushed to ovirt-engine-3.5, so this is not
an issue there.

Change-Id: Iafe35b1f4bdbee8068ea79629342518ca3405a62
Signed-off-by: Lior Vernia <lvernia@redhat.com>