Most python tests windows

[cgravill]

No description provided.

[cgravill]

A subset of the Python tests now pass on Windows!

It's notably not running the TorchScript2Knossos tests see #659 or the direct GCC/pybind tests.

I had to do some ugly things with pinning to an earlier version of pip and using the legacy resolver as the new resolver interacts poorly with PyTorch version numbers.
https://pip.pypa.io/en/latest/user_guide/#changes-to-the-pip-dependency-resolver-in-20-3-2020

Note: I don't reproduce this breakage locally (on Windows, or Ubuntu) so it may be only on Python 3.7 (on Windows or the particular set-up of the devops machines). Also had to disable the cache directory per:
https://stackoverflow.com/a/31526029/35544

We might want to separately make these Pip changes/pinning to the Linux build for consistency / safety.

[awf]

Fab, thanks!