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: I97d1a72fa4b6d61c82317cc91405d5e68a719119
diff --git a/setup.cfg b/setup.cfg
index 7866a06..6ad7813 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,11 +1,11 @@
 [metadata]
 name = cinder-tempest-plugin
 summary = Tempest plugin tests for Cinder.
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = http://www.openstack.org/
+author_email = openstack-discuss@lists.openstack.org
+home_page = http://www.openstack.org/
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology