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] https://github.com/pypa/setuptools/commit/a2e9ae4cb

Change-Id: If5cb829ef8530690f9208f9b15915e2c17367190
diff --git a/setup.cfg b/setup.cfg
index 144569f..136aa0f 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,12 +1,12 @@
 [metadata]
 name = neutron-tempest-plugin
 summary = Tempest plugin for Neutron Project
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = https://opendev.org/openstack/neutron-tempest-plugin
-python-requires = >=3.6
+author_email = openstack-discuss@lists.openstack.org
+home_page = https://opendev.org/openstack/neutron-tempest-plugin
+python_requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology