def add_publisher(publisher)
      @master.register_publisher(publisher.topic_name,
                                 publisher.topic_type.type)
      publisher.set_manager(self)
      @publishers.push(publisher)
      publisher
    end
def add_publisher(publisher)
      @master.register_publisher(publisher.topic_name,
                                 publisher.topic_type.type)
      publisher.set_manager(self)
      @publishers.push(publisher)
      publisher
    end
register a publisher. raise if fail.
 @param [Publisher] publisher Publisher instance to be added
 @return [Publisher] publisher