[SPARK-1840] SparkListenerBus prints out scary error message when terminated normally

Running SparkPi example gave this error.
```
Pi is roughly 3.14374
14/05/14 18:16:19 ERROR Utils: Uncaught exception in thread SparkListenerBus
scala.runtime.NonLocalReturnControl$mcV$sp
```
This is due to the catch-all in the SparkListenerBus, which logged control throwable used by scala system

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #783 from tdas/controlexception-fix and squashes the following commits:

a466c8d [Tathagata Das] Ignored control exceptions when logging all exceptions.