Modify  TachyonWorker Heartbeat sleeping to ScheduledExecutorService 

TachyonWorker's heartbeat thread is sleeping several milliseconds . 
JDK API ScheduledExecutorService's scheduleAtFixedRate method running a task after initial delay and subsequently with the given period. It's more fit for the heartbeat task .
And a TODO : split heartbeat thread into another class.
thanks 
you mean mMasterInfo.init() in TachyonMaster ? In HeartbeatThread's run function sleeping a small interval . Maybe should create a abstract heartbeat service for both master and worker ?