[SPARK-2322] Exception in resultHandler should NOT crash DAGScheduler and shutdown SparkContext.

This should go into 1.0.1. 
Could we wrap a wider area with this try-catch? For instance, we've also had problems where Accumulators.add throws an exception, and we similarly don't want the entirety of Spark to crash. I think any unhandled exception in the handleTaskCompletion method deserves a task failure.