Investigate the use case of slurm `sacct`

It seems `aiida-core` is using this to get the exit code in a complicated manner:

`tasks.py` and `calcjob.py` both expect a dictionary with three keys (`'retval'`,   `'stdout'`,   `'stderr'`) from:
`scheduler.get_detailed_job_info()`
Which then `calcjob.py` uses it along with two other files to call again on `scheduler.parse_output` to get the exit code. 
