a802e84cd5
This provides incremental output when test is running _without xdist_,
just like the old runner did.
With xdist the live output is not available, I believe because of
https://github.com/pytest-dev/pytest-xdist/issues/402
https://github.com/pytest-dev/pytest-xdist/pull/883 might help with
that, but I'm not going to hold my breath until it is available on
distros we use.
(cherry picked from commit d0619c7a18)