Track workers by executor ID instead of hostname to allow multiple

core/src/main/scala/spark/MapOutputTracker.scala

core/src/main/scala/spark/SparkContext.scala

core/src/main/scala/spark/SparkEnv.scala

core/src/main/scala/spark/deploy/LocalSparkCluster.scala

core/src/main/scala/spark/deploy/master/Master.scala

core/src/main/scala/spark/deploy/worker/ExecutorRunner.scala

core/src/main/scala/spark/executor/Executor.scala

.../src/main/scala/spark/executor/MesosExecutorBackend.scala

...main/scala/spark/executor/StandaloneExecutorBackend.scala

core/src/main/scala/spark/scheduler/DAGScheduler.scala

core/src/main/scala/spark/scheduler/DAGSchedulerEvent.scala

core/src/main/scala/spark/scheduler/MapStatus.scala

core/src/main/scala/spark/scheduler/Stage.scala

...rc/main/scala/spark/scheduler/TaskSchedulerListener.scala

...main/scala/spark/scheduler/cluster/ClusterScheduler.scala

...spark/scheduler/cluster/SparkDeploySchedulerBackend.scala

.../spark/scheduler/cluster/StandaloneSchedulerBackend.scala

.../main/scala/spark/scheduler/cluster/TaskDescription.scala

core/src/main/scala/spark/scheduler/cluster/TaskInfo.scala

...c/main/scala/spark/scheduler/cluster/TaskSetManager.scala