docs: def __StartMaster(self):
      """ Starts a master node, configures it, and starts services. """    
      num_masters = len(self.cluster.get_instances_in_role("master", "running"))
      assert(num_masters < 1)
      logging.info( "waiting for masters to start")
      if self.config.master_on_spot_instances:          
        self.__LaunchSpotMasterInstances()
      else:
        self.__LaunchOnDemandMasterInstances()
      time.sleep(1)
      self.__ConfigureMaster()
      return True