[BZ 1139267] - Undeploy Selected button on Storage Nodes page is disabled so it's not possible to remove second storage node - there was an error when checking if the storage node is available

(cherry picked from commit cf1fca873c0f8a59650b0c99fbc138e79626d719)
Signed-off-by: Libor Zoubek <lzoubek@redhat.com>