Speed up test suite via distributed testing (#2196)

* Speed up test suite via distributed testing

Since we now run the test suite twice, one with Python 2 and another
without, full test runs are getting pretty slow. Let's try to
fix that with parallization.

Also use verbose mode on CI since more logs is usually better since
getting more is quite literally impossible.

The main issue we'll face with this is we'll hit
https://github.com/pytest-dev/pytest-xdist/issues/620 sometimes
(although pretty rarely). I suppose we can test this and see if how bad
this bug is for us, and revert if necessary down the line.

Also let's have some colours 🎉