Tasks never complete due to SLURM cache clearing too quickly.

[FrankD412]

In some instances when the SLURM job cache is behaving erratically or removes completed jobs from the squeue cache too quickly, it leaves finishing jobs in an UNKNOWN state, resulting in the state being left in RUNNING. The appropriate guess here for the FINISHING state would be to assume the job finished and set it accordingly.

Found when testing #263