Add pack_job_id and pack_job_offset to job records

Add pack_job_id and pack_job_offset fields to job record in slurmctld
  plus job_info structure
Add logic to save/restore pack_job_id and pack_job_offset fields on
  slurmctld restart
Add logging of pack_job_id and pack_job_offset fields in slurmctld's
  jobid2fmt() and jobid2str() functions
Add pack_job_id and pack_job_offset fields to "scontrol show job"
  output