backup slurmctld treats dupl job state file fatal

If the backup slurmctld assumes primary status, then do NOT purge any
job state files (batch script and environment files) but if any attempt
is made to re-use them consider this a fatal error. It may indicate that
multiple primary slurmctld daemons are active (e.g. both backup and primary
are functioning as primary and there is a split brain problem).