Replace old 'master' term with 'driver'.

bagel/src/test/scala/bagel/BagelSuite.scala

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

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

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

.../src/main/scala/spark/broadcast/BitTorrentBroadcast.scala

core/src/main/scala/spark/broadcast/Broadcast.scala

core/src/main/scala/spark/broadcast/BroadcastFactory.scala

core/src/main/scala/spark/broadcast/HttpBroadcast.scala

core/src/main/scala/spark/broadcast/MultiTracker.scala

core/src/main/scala/spark/broadcast/TreeBroadcast.scala

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

core/src/main/scala/spark/deploy/client/ClientListener.scala

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

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

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

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

...la/spark/scheduler/cluster/StandaloneClusterMessage.scala

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

...a/spark/scheduler/mesos/CoarseMesosSchedulerBackend.scala

core/src/main/scala/spark/storage/BlockManagerMaster.scala