[sapphire] "thread.error: release unlocked lock" following Ctrl-C on macos

[jschwartzentruber]

Seen after Ctrl-C:

Traceback (most recent call last):
  File "/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/Users/truber/grizzly-auto-run/grizzly/grizzly/__main__.py", line 13, in <module>
    sys.exit(console_main())
  File "/Users/truber/grizzly-auto-run/grizzly/grizzly/main.py", line 53, in console_main
    return main(GrizzlyArgs().parse_args())
  File "/Users/truber/grizzly-auto-run/grizzly/grizzly/main.py", line 152, in main
    session.run()
  File "/Users/truber/grizzly-auto-run/grizzly/grizzly/session.py", line 180, in run
    optional_files=current_test.get_optional())
  File "/Users/truber/grizzly-auto-run/grizzly/sapphire/core.py", line 530, in serve_path
    while not job.is_complete(wait=0.5):
  File "/Users/truber/grizzly-auto-run/grizzly/sapphire/core.py", line 163, in is_complete
    return self._complete.wait(wait)
  File "/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 615, in wait
    return self.__flag
  File "/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 289, in __exit__
    return self.__lock.__exit__(*args)
thread.error: release unlocked lock