[SPARK-4067] refactor ExecutorUncaughtExceptionHandler

https://issues.apache.org/jira/browse/SPARK-4067

currently , we call Utils.tryOrExit everywhere
AppClient
Executor
TaskSchedulerImpl
It makes the name of ExecutorUncaughtExceptionHandler unfit to the real case....

Author: Nan Zhu <nanzhu@Nans-MacBook-Pro.local>
Author: Nan Zhu <nanzhu@nans-mbp.home>

Closes #2913 from CodingCat/SPARK-4067 and squashes the following commits:

035ee3d [Nan Zhu] make RAT happy
e62e416 [Nan Zhu] add some general Exit code
a10b63f [Nan Zhu] refactor
[GraphX] Modify option name according to example doc in SynthBenchmark

Now graphx.SynthBenchmark example has an option of iteration number named as "niter". However, in its document, it is named as "niters". The mismatch between the implementation and document causes certain IllegalArgumentException while trying that example.

Author: Grace <jie.huang@intel.com>

Closes #2888 from GraceH/synthbenchmark and squashes the following commits:

f101ee1 [Grace] Modify option name according to example doc