project manager job caching

[johrstrom]

While working on #3473 I found that we likely need to cache jobs so we don't query the scheduler over and over. The job_history.log has a list of all the jobs that the launcher has created - but we need some sort of way to track job state as well. Specifically completed. We can requery for active jobs (jobs that are not complete) but we shouldn't be querying for jobs that are already complete. without some sort of mechanism to save the jobs' state, we'll overload the scheduler.