Add LocalSparkContext to manage common sc variable.

core/src/test/scala/spark/AccumulatorSuite.scala

core/src/test/scala/spark/BroadcastSuite.scala

core/src/test/scala/spark/CheckpointSuite.scala

core/src/test/scala/spark/ClosureCleanerSuite.scala

core/src/test/scala/spark/DistributedSuite.scala

core/src/test/scala/spark/FailureSuite.scala

core/src/test/scala/spark/FileServerSuite.scala

core/src/test/scala/spark/FileSuite.scala

core/src/test/scala/spark/LocalSparkContext.scala

core/src/test/scala/spark/MapOutputTrackerSuite.scala

core/src/test/scala/spark/PartitioningSuite.scala

core/src/test/scala/spark/PipedRDDSuite.scala

core/src/test/scala/spark/RDDSuite.scala

core/src/test/scala/spark/ShuffleSuite.scala

core/src/test/scala/spark/SortingSuite.scala

core/src/test/scala/spark/ThreadingSuite.scala

core/src/test/scala/spark/scheduler/TaskContextSuite.scala