Each process races to set up its virtualenv in the same place.

Probably needs more flock -- but how to make it work cross platform?

@chriskuehl hits this a lot.
@ymilki just hit this as well

Workaround is to run once not-in-parallel and then it'll just work

Stacktraces vary, some complain of directories already existing An unexpected error has occurred: OSError: [Errno 39] Directory not empty: '.../.pre-commit/repop35TZY/py_env-default'