Renamed getJobSummary call to getRoleSummary

getJobSummary will be reused to return the jobs.

Testing Done:
gradle clean build
gradle run and tested on my laptop

Bugs closed: AURORA-64

Reviewed at https://reviews.apache.org/r/18340/
Prepare and launch GC executor tasks asynchronously.

Bugs closed: AURORA-214

Reviewed at https://reviews.apache.org/r/18141/