Feature/re chdir on restart

I like not cleaning up on failure, it allows you to figure out what went wrong!

But it doesn't clean up on success, either, maybe I should do that, but I think a bunch of the tests leave logs and other ephemera around.

I could put the symlink in strong-supervisor/test/ instead of strong-supervisor/, if it would make a difference to any of our tooling, or even to people.