Let OCG do file cleanup

We have a garbage collection thread which runs every 6 hours to clean
up redis and the file system. By default we tolerate max lifetimes of
- redis job status hash objects, 5 days
- completed job files, 5.5 days (/srv/deployment/ocg/output)
- failed job status objects in redis, 0.5 day
- objects on the temp file system, 0.5 day (/mnt/tmpfs)
- postmortem files, 5 days (/srv/deployment/ocg/postmortem)

Change-Id: I5285f3ff091d4f889b0d683f5129eef54f6633d5