Add tests for FileLogger, EventLoggingListener, and ReplayListenerBus

Modifications to Spark core are limited to exposing functionality to test files + minor style fixes.
(728 / 769 lines are from tests)

Author: Andrew Or <andrewor14@gmail.com>

Closes #591 from andrewor14/event-log-tests and squashes the following commits:

2883837 [Andrew Or] Merge branch 'master' of github.com:apache/spark into event-log-tests
c3afcea [Andrew Or] Compromise
2d5daf8 [Andrew Or] Use temp directory provided by the OS rather than /tmp
2b52151 [Andrew Or] Remove unnecessary file delete + add a comment
62010fd [Andrew Or] More cleanup (renaming variables, updating comments etc)
ad2beff [Andrew Or] Clean up EventLoggingListenerSuite + modify a few comments
862e752 [Andrew Or] Merge branch 'master' of github.com:apache/spark into event-log-tests
e0ba2f8 [Andrew Or] Fix test failures caused by race condition in processing/mutating events
b990453 [Andrew Or] ReplayListenerBus suite - tests do not all pass yet
ab66a84 [Andrew Or] Tests for FileLogger + delete file after tests
187bb25 [Andrew Or] Formatting and renaming variables
769336f [Andrew Or] Merge branch 'master' of github.com:apache/spark into event-log-tests
5d38ffe [Andrew Or] Clean up EventLoggingListenerSuite + add comments
e12f4b1 [Andrew Or] Preliminary tests for EventLoggingListener (need major cleanup)