Prior to this change, we were pre-maturely stopping a worker (since it
was deemed redundant under a race condition), and then we immediately
created a new worker with the same hash to finish off the test run. The
worker creation is expensive, so this slowed down the overall test run
time.
See the following for logs of the old code illustrating the extra stops and starts: https://gist.github.com/rwoll/1c592ed9e8f9169274fa972674de6703
d1ae23c750