run-tests: enable color on Windows
In setting up the CI for Windows on heptapod, I noticed it was complaining about
color not being enabled because pygments wasn't installed- even though it was.
I had initially disabled color on Windows when using Windows 7, because that
didn't understand ANSI color codes and made a mess of the output. But now that
it's been unsupported for over a year, I don't think we should care about it
It's admittedly a hack to depend on Mercurial proper to enable color support in
the terminal, but I didn't feel like duplicating that code. I'm under the
impression that 3rd party stuff is supposed to use this runner in the Mercurial
repo instead of using their own copy, so I think it's safe to assume the
Mercurial code is available. If it's not, it won't break anything.
Differential Revision: https://phab.mercurial-scm.org/D10760