def unregister_publisher(topic)
      code, message, val = @proxy.unregisterPublisher(@caller_id,
                                                      topic,
                                                      @slave_uri)
      if code == 1
        return val
      elsif code == 0
        puts message
        return true
      else
        raise message
      end
      return false
    end
def unregister_publisher(topic)
      code, message, val = @proxy.unregisterPublisher(@caller_id,
                                                      topic,
                                                      @slave_uri)
      if code == 1
        return val
      elsif code == 0
        puts message
        return true
      else
        raise message
      end
      return false
    end
unregister a publisher
 @param [String] topic name of topic
 @return [Boolean] true
 @raise RuntimeError