def register_subscriber(topic, topic_type)
      code, message,val = @proxy.registerSubscriber(@caller_id,
                                                    topic,
                                                    topic_type,
                                                    @slave_uri)
      if code == 1
        val
      elsif code == 0
        puts message
        val
      else
        raise message
      end
    end
def register_subscriber(topic, topic_type)
      code, message,val = @proxy.registerSubscriber(@caller_id,
                                                    topic,
                                                    topic_type,
                                                    @slave_uri)
      if code == 1
        val
      elsif code == 0
        puts message
        val
      else
        raise message
      end
    end
register a subscriber
 @param [String] topic topic name
 @param [String] topic_type topic type
 @return [Array] URI of current publishers
 @raise [RuntimeError] if error