[SPARK-4013] Do not create multiple actor systems on each executor

In the existing code, each coarse-grained executor has two concurrently running actor systems. This causes many more error messages to be logged than necessary when the executor is lost or killed because we receive a disassociation event for each of these actor systems.

This is blocking #2840.

Author: Andrew Or <andrewor14@gmail.com>

Closes #2863 from andrewor14/executor-actor-system and squashes the following commits:

44ce2e0 [Andrew Or] Avoid starting two actor systems on each executor
[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
[HOTFIX][SQL] Remove sleep on reset() failure.

Author: Michael Armbrust <michael@databricks.com>

Closes #2934 from marmbrus/patch-2 and squashes the following commits:

a96dab2 [Michael Armbrust] Remove sleep on reset() failure.