cherry-picker: Run Travis CI test on Windows

[encukou]

I've set up a Windows build on Travis before, maybe I can help #296 a bit!
There's no Python pre-installed, but there's a package manager, choco, that can install it.

Currently, the tests fail because they seem to require Git's user.email and user.name to be set globally. They fail on my dev machine as well, since I don't have an e-mail set globally (I use different e-mail addresses on different repos).
Sadly, I can't devote time to fixing that issue, but I can help to reproduce or explain more if needed.

To try out changes privately, here's what I do:

• Enable Travis on your fork of the repo
• Uncheck "Build pused branches" and "Build pushed pull requests" on your fork's Travis settings (you'll want to trigger builds manually)
• Push code you want to test to your fork's master branch
• Use "Trigger build in Travis's "More options" menu to trigger the build
• Cancel any builds you're not interested in (for example, all the Linux builds) to save both time and processing

[webknjaz]

It should be easy to fix tests by extending this fixture (https://github.com/python/core-workflow/blob/b3c68fe/cherry_picker/cherry_picker/test.py#L87-L91) to set local user and email in config.

[encukou]

Oh, one more thing I meant to put in the initial comment:

Unfortunately I probably won't find much time to tend to this PR properly. Feel free to make changes directly to the branch, that'll make things much faster.

[webknjaz]

Another thing is that Travis CI seems to be going down now: ansible/molecule#1770

[webknjaz]

Git config related tests fixed. Now, there's two Unicode-related failures.

[webknjaz]

@Mariatta please merge it, it's ready.

[Mariatta]

Thanks!!