Refuse to set tasks to failed if shutting down
Refuse to set tasks to failed if shutting down

If we are shutting down, the task most likely has not actually failed,
and the child process(es) was/were killed because of the shutdown.  This
should not count towards the failure count of the current tasks.

guidow/pyfarm-agent,pyfarm/pyfarm-agent,guidow/pyfarm-agent,pyfarm/pyfarm-agent,guidow/pyfarm-agent,pyfarm/pyfarm-agent