Spark driver failed with NPE on job cancelation

When a job group is cancelled, we scan through all jobs to determine which are members of the group. This scan assumes that the job group property is always set. If 'properties' is null in an active job, you get an NPE.

We just need to make sure we ignore ones where activeJob.properties is null. We should also make sure it works if the particular property is missing.

https://github.com/apache/spark/blob/branch-1.3/core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala#L678