ci:use pytest-xdist to parallelize tests

[alexrudd2]

https://pypi.org/project/pytest-xdist/

Also I'm pretty sure -s has no effect since Pytest 3.4

[oroulet]

Does it handle having some servers run on the same port?
At least it looks like the failed tests are releated to something different....

[alexrudd2]

It doesn't do anything automatically (besides run tests in parallel). So the tests might have to be changed to use different ports.

In the past I've used @pytest.mark.parameterize to do this but I'm not sure how these tests are setup.

[alexrudd2]

What about binding to port 0, which will cause the OS to assign a random available port? After the server is created, the assigned port can be determined with srv.bserver.port and given to the client.