code: def register_on_guest_property_changed(self, callback):
          
          event_type = library.VBoxEventType.on_guest_property_changed
          return self.event_source.register_callback(callback, event_type)
docs: Set the callback function to consume on guest property changed
          events.
  
          Callback receives a IGuestPropertyChangedEvent object.
  
          Returns the callback_id