[SPARK-5655] Don't chmod700 application files if running in YARN

[Was previously PR4507]

As per SPARK-5655, recently committed code chmod 700s all application files created on the local fs by a spark executor. This is both unnecessary and broken on YARN, where files created in the nodemanager's working directory are already owned by the user running the job and the 'yarn' group. Group read permission is also needed for the auxiliary shuffle service to be able to read the files, as this is running as the 'yarn' user.

Author: Andrew Rowson <github@growse.com>

Closes #4509 from growse/master and squashes the following commits:

7ca993c [Andrew Rowson] Moved chmod700 functionality into Utils.getOrCreateLocalRootDirs
f57ce6b [Andrew Rowson] [SPARK-5655] Don't chmod700 application files if running in a YARN container