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: I7e93878229258afee7eb67cc652f30f63702ab41

setup.cfg

@@ -1,12 +1,12 @@
 [metadata]
 name = ec2-api
 summary = OpenStack Ec2api Service
-description-file =
+description_file =
     README.rst
 license = Apache License, Version 2.0
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = https://launchpad.net/ec2-api
+author_email = openstack-discuss@lists.openstack.org
+home_page = https://launchpad.net/ec2-api
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology