setup.cfg: Replace dashes with underscores
setup.cfg: Replace dashes with underscores

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 [1].
Get ahead of the issue by replacing the dashes with underscores.
Without this, we see 'UserWarning' messages
like the following on new enough
versions of setuptools:

  UserWarning: Usage of dash-separated 'description-file' will not be
  supported in future versions. Please use the underscore name
  'description_file' instead

Change-Id: I0f6367719b67e543a3abe0bb649f8cae290fd7cd

openstack/release-test