def add_service_server(service_server)
      @master.register_service(service_server.service_name,
                               service_server.service_uri)
      service_server.set_manager(self)
      @service_servers.push(service_server)
      service_server
    end
def add_service_server(service_server)
      @master.register_service(service_server.service_name,
                               service_server.service_uri)
      service_server.set_manager(self)
      @service_servers.push(service_server)
      service_server
    end
register a service to master,
 and add it in the controlling server list.
 raise if fail.
 @param [ServiceServer] service_server ServiceServer to be added
 @return [ServiceServer] service_server