tests/test-debugrename.t

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

  $ hg init
  $ echo a > a
  $ hg ci -Am t
  adding a

  $ hg mv a b
  $ hg ci -Am t1
  $ hg debugrename b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3

  $ hg mv b a
  $ hg ci -Am t2
  $ hg debugrename a
  a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980

  $ hg debugrename --rev 1 b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3