tests: make test-worker.t pass on py2 I broke the py2 version in https://phab.mercurial-scm.org/D9287 because the `WorkerError.__bytes__()` (or `.__str__()`?) output was different in py2 compared to py3. Part of the problem was that I didn't propagate the status code that was passed in to the superclass so it could get printed. This patch fixes that. I don't know how it worked on py3 before this patch... I also added the usual `__bytes__ = _tobytes` override for good measure. It doesn't seem to be needed for tests to pass, though. Differential Revision: https://phab.mercurial-scm.org/D9377