continue to refactor code style and functions

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

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

...ain/scala/spark/deploy/master/MasterInstrumentation.scala

...ain/scala/spark/deploy/worker/WorkerInstrumentation.scala

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

...c/main/scala/spark/executor/ExecutorInstrumentation.scala

core/src/main/scala/spark/metrics/MetricsConfig.scala

core/src/main/scala/spark/metrics/MetricsSystem.scala

core/src/main/scala/spark/metrics/sink/ConsoleSink.scala

core/src/main/scala/spark/metrics/sink/CsvSink.scala

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

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

core/src/test/scala/spark/metrics/MetricsConfigSuite.scala

core/src/test/scala/spark/metrics/MetricsSystemSuite.scala