msys2 python2 for running tests

Hi Herbert, I saw your comment on the Windows build page about msys2's python2. It used to be broken, a patch of mine recently went through to fix the problem. If you can verify that msys2's python2 works correctly for the entire test suite, feel free to update the instructions https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows accordingly. Also, it looks like you added a section for setting up sshd on msys2. I think it's great, but I don't think it should be on the main ghc build page, it's just a separate concern (and it's also interesting not just to people building ghc). Would you mind moving that text off to a separate wikipage and adding a link to it instead? -- Gintautas Miliauskas