Differentiate between the return values

[mathisloevenich]

As jobs are executed, the will eventually have return values of the executed function ≠ 0, which could be valuable for the user.
These jobs could also be collected under a "state", regarding #112

[mathisloevenich]

HTCondor exit codes can be found here:
https://htcondor.readthedocs.io/en/latest/codes-other-values/condor_shadow-exit-codes.html