code: def add_event_handler(self, action):
          
          if action.uuid in self.actions:
              logger.info("Already existing event handler: %s", action)
              return
  
          self.actions[action.uuid] = action
          self.nb_event_handlers += 1
docs: Add a event handler into actions list
  
          :param action: event handler to add
          :type action: alignak.eventhandler.EventHandler
          :return: None