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

[1] pypa/setuptools@a2e9ae4cb

Change-Id: I4f5ebb221bb305ec82aaa94829c2b16f72fa7a3c

Author: yangyawei

setup.cfg

@@ -1,11 +1,11 @@
 [metadata]
 name = cloudkitty-dashboard
 summary = CloudKitty Horizon dashboard
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = [email protected]
-home-page = https://docs.openstack.org/cloudkitty-dashboard/latest/
+author_email = [email protected]
+home_page = https://docs.openstack.org/cloudkitty-dashboard/latest/
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology