Slurm was complaining because threadring was calling exit(0).  Cause that not
to happen, and note that these tests will have it happen if they are run with
Slurm.
Merge pull request #472 from lydia-duncan/silenceThreadringSlurm

Fix threadring slurm complaint

Slurm was complaining because threadring was calling exit(0). Cause that not
to happen, and note that these tests will have it happen if they are run with
Slurm.