PM-697 Exposed a property pegasus.file.cleanup.clusters.size per Yu's
request to control the number of cleanup jobs that get clustered into
a bigger cleanup job.
Merge branch 'PM-697' added the new property pegasus
pegasus.file.cleanup.clusters.size to control the numnber of jobs
clustered into a bigger clustered job.
Merge branch 'master' of https://github.com/pegasus-isi/pegasus