Prevent exception in listener.

Exception in thread "SparkListenerBus" java.util.NoSuchElementException: key not found: 11229
	at scala.collection.MapLike$class.default(MapLike.scala:228)
	at scala.collection.AbstractMap.default(Map.scala:58)
	at scala.collection.mutable.HashMap.apply(HashMap.scala:64)
	at org.apache.spark.ui.jobs.JobProgressListener.onStageCompleted(JobProgressListener.scala:68)
	at org.apache.spark.scheduler.SparkListenerBus$$anon$2$$anonfun$run$2.apply(SparkListenerBus.scala:47)
	at org.apache.spark.scheduler.SparkListenerBus$$anon$2$$anonfun$run$2.apply(SparkListenerBus.scala:47)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at org.apache.spark.scheduler.SparkListenerBus$$anon$2.run(SparkListenerBus.scala:47)
Changes to testcode to more exhaustively verify
Modification to when executor is added to failedExecutors : we saw some cases where it was slipping through our checks and causing entire job to fail