to permit user control over exit codes so application exit codes can be
    distiguished from those generated by SLURM. SLURM_ERROR_EXIT specifies the
    exit code when a SLURM error occurs. SLURM_IMMEDIATE_EXIT specifies the 
    exit code when the --immediate option is specified and resources are not
    available. Any other non-zero exit code would be that of the application
    run by SLURM.