webadmin: Don't apply SuggestBox selection on tab

The default behavior where pressing tab applies the selected
suggestion isn't desireable for us, so the event propagation is
stopped in that case.

Change-Id: I13e67506f8b2b93fb97189392582175df7582917
Bug-Url: https://bugzilla.redhat.com/1134208
Signed-off-by: Lior Vernia <lvernia@redhat.com>