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: Ie1a033f1dcb1b62bf1bc8a213b9d7ef7e4e5b299

openstack/ceilometer,openstack/ceilometer