Bug 942720 - Fix test_settings_airplane_mode.py

The UI will 
1) display "Connected to {{ssid}}" in a short time, 
2) then change to "Connected to Mozilla Guest".

The gaia-ui-tests will pass the following statement at step 1 and failed the test:
  self.wait_for_condition(lambda s: 'Connected' in settings.wifi_menu_item_description, timeout=40)