* Setuptools v54.1.0 introduces a warning that the use of dash-separated
options in 'setup.cfg' will not be supported in a future version .
Get ahead of the issue by replacing the dashes with underscores.Without
this, we see 'UserWarning' messages.
* Replace .testr.conf by .stestr.conf for migration and update
.gitignore and test-requirements.txt file accordingly
* Use py3 as the default runtime for tox
* Add a new job, openstack-cover-jobs, to run the coverage in Zuul