webadmin: fix button availability for qos subtab

Change-Id: Ia91804df19b82c579254b8e87e5894133e74e7a3
Bug-Url: https://bugzilla.redhat.com/1142815
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>
(cherry picked from commit 11d032c5587351730102a96ec04245bd5f0aa736)