Use underscores instead of dashes in setup.cfg

We've been seeing warnings like

    UserWarning: Usage of dash-separated 'home-page' will not be supported
    in future versions. Please use the underscore name 'home_page' instead

for a while in our pep8 jobs; this ought to clean them up. As best I can
tell, setuptools has supported either format for several years.

Change-Id: I4d538859f278ac26a6b6d6845df103ebd4c49da3

setup.cfg

@@ -1,11 +1,11 @@
 [metadata]
 name = swift
 summary = OpenStack Object Storage
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = https://docs.openstack.org/swift/latest/
+author_email = openstack-discuss@lists.openstack.org
+home_page = https://docs.openstack.org/swift/latest/
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: OpenStack