hostname里不能包含"_"，否则报错
INFO RemoteActorRefProvider$RemoteDeadLetterActorRef: Message [org.apache.spark.deploy.DeployMessages$RegisterWorker] from Actor[akka://sparkWorker/user/Worker#-1461285761] to Actor[akka://sparkWorker/deadLetters] was not delivered. [3] dead letters encountered. This logging can be turned off or adjusted with configuration settings ‘akka.log-dead-letters‘ and ‘akka.log-dead-letters-during-shutdown‘.
ERROR Worker: All masters are unresponsive! Giving up.
原文：http://my.oschina.net/MaTech/blog/336510