- The job's life-cycle is now tracked in attempt.status, which simplifies
  job.status (a single 'IN_PROGRESS' status).
- The job_file functionality is now tracked in the attempt table, and
  attempt_id is used in several tables instead of job_id/role_id
- job.when_completed is the same as attempt.when_updated (for the last
  successful) attempt)
- job.retry_count is removed as it is very tricky to maintain. Instead it
  is computed on the fly when needed
- last_attempt_id tells us whether the job has ever been tried or not
- Remove the unused 'COMPILATION' job status