SPARK-1557 Set permissions on event log files/directories

This adds minimal setting of event log directory/files permissions.  To have a secure environment the user must manually create the top level event log directory and set permissions up.   We can add logic to do that automatically later if we want.

Author: Thomas Graves <tgraves@apache.org>

Closes #538 from tgravescs/SPARK-1557 and squashes the following commits:

e471d8e [Thomas Graves] rework
d8b6620 [Thomas Graves] update use of octal
3ca9b79 [Thomas Graves] Updated based on comments
5a09709 [Thomas Graves] add in missing import
3150ed6 [Thomas Graves] SPARK-1557 Set permissions on event log files/directories