Use a modern fixture instead of removed cached_setup (pytest 4.1)
Use a modern fixture instead of removed cached_setup (pytest 4.1)

This require us to remove the --gwscope option because we won't
be able to parametrize the fixture based on the deprecated
'pytest.config' variable

Also remove pytest_report_header: it was displaying the removed "scope" option
and execnet's version, which seems odd and not very useful nowadays

WIP

alfredodeza/execnet,pytest-dev/execnet