[SPARK-16522][MESOS] Spark application throws exception on exit.

## What changes were proposed in this pull request?
Spark applications running on Mesos throw exception upon exit. For details, refer to https://issues.apache.org/jira/browse/SPARK-16522.

I am not sure if there is any better fix, so wait for review comments.

## How was this patch tested?
Manual test. Observed that the exception is gone upon application exit.

Author: Sun Rui <sunrui2016@gmail.com>

Closes #14175 from sun-rui/SPARK-16522.