Author: Jongyoul Lee <jongyoul@gmail.com>

Closes #3897 from jongyoul/SPARK-5088 and squashes the following commits:

8232aa8 [Jongyoul Lee] [SPARK-5088] Use spark-class for running executors directly - Added a listenerBus for fixing test cases
932289f [Jongyoul Lee] [SPARK-5088] Use spark-class for running executors directly - Rebased from master
613cb47 [Jongyoul Lee] [SPARK-5088] Use spark-class for running executors directly - Fixed code if spark.executor.uri doesn't have any value - Added test cases
ff57bda [Jongyoul Lee] [SPARK-5088] Use spark-class for running executors directly - Adjusted orders of import
97e4bd4 [Jongyoul Lee] [SPARK-5088] Use spark-class for running executors directly - Changed command for using spark-class directly - Delete sbin/spark-executor and moved some codes into spark-class' case statement