webadmin: Resize ListModelTypeAheadListBox for consistency

Resized this widget to be consistent with other widgets.

Change-Id: Ib2532daf8390a05f07203140ef8857d1207ba6dd
Bug-Url: https://bugzilla.redhat.com/1127582
Signed-off-by: Lior Vernia <lvernia@redhat.com>