[Hot Fix #469] Fix flaky test in SparkListenerSuite

The two modified tests may fail if the race condition does not bid in our favor...

Author: Andrew Or <andrewor14@gmail.com>

Closes #516 from andrewor14/stage-info-test-fix and squashes the following commits:

b4b6100 [Andrew Or] Add/replace missing waitUntilEmpty() calls to listener bus
Update Java api for setJobGroup with interruptOnCancel

Also adds a unit test.

Author: Aaron Davidson <aaron@databricks.com>

Closes #522 from aarondav/cancel2 and squashes the following commits:

565c253 [Aaron Davidson] Update Java api for setJobGroup with interruptOnCancel
65b33d8 [Aaron Davidson] Add unit test for Thread interruption on cancellation
Mark all fields of EdgePartition, Graph, and GraphOps transient

These classes are only serializable to work around closure capture, so their fields should all be marked `@transient` to avoid wasteful serialization.

This PR supersedes apache/spark#519 and fixes the same bug.

Author: Ankur Dave <ankurdave@gmail.com>

Closes #520 from ankurdave/graphx-transient and squashes the following commits:

6431760 [Ankur Dave] Mark all fields of EdgePartition, Graph, and GraphOps `@transient`