Add explain plan to Hive on Spark Web UI

More of an investigation JIRA. The Spark UI has a "long description" of each stage in the Spark DAG. Typically one stage in the Spark DAG corresponds to either a MapWork or ReduceWork object. It would be useful if the long description contained the explain plan of the corresponding work object.

I'm not sure how much additional overhead this would introduce. If not the full explain plan, then maybe a modified one that just lists out all the operator tree along with each operator name.