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

Resolves warnings like the following:

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

Change-Id: I328d2e7843e3ba62a6de4ef221c4f8564a64f234

openstack/cliff,openstack/cliff