Add pydantics requirements all.txt test

The added test compares pip's with monotrail's requirements.txt installation and checks that filenames and file contents are identical to the point that that makes sense.

The current test setup has two problems, namely that it's slow and that it uses the internet for both pip and monotrail. This is more realistic (when pypi changes our tests start pick that up), but also fragile and slow. It would be cool to have both pip and monotrail use a local cache or a proxy. For pip i don't know how to coerce it into using fixed data except starting or own pypi mirror/proxy, for monotrail we should eiter use a request mock or a local cache dir with a no refresh option.

konstin / poc-monotrail

Add pydantics requirements all.txt test #46