tests: stabilize test-persistent-nodemap.t on Windows
Several issues here:
- Hooks can't invoke shell scripts on Windows, so use `sh` to launch
- `dd` in MSYS only recognizes `status=noxfer`
- The `PATH` updating triggered a massive slowdown, but is no longer needed
I have no idea why, but removing the `PATH` update substantially increased the
speed of the test. It was running finishing at ~4:30 with `--debug` and ~14:50
without it, but now completes in ~2:20 on my Windows laptop.
Differential Revision: https://phab.mercurial-scm.org/D10636
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