Update metadata in setup.cfg

we are using some "aliases" that the setuptools docs say 
"are supported for compatibility reasons" but their use is not advised[1].

[1] https://setuptools.pypa.io/en/latest/userguide/declarative_config.html#metadata

maintaining setup.cfg as per other repos[2]

[2] https://review.opendev.org/c/openstack/cinder-specs/+/822918

example : https://github.com/pypa/virtualenv/blob/main/setup.cfg

Change-Id: I992fc9c81a08474a04373ad1bfd710988517f0b8
diff --git a/setup.cfg b/setup.cfg
index 3b246b5..3f37df9 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,13 +1,12 @@
 [metadata]
 name = cinder-tempest-plugin
-summary = Tempest plugin tests for Cinder.
-description_file =
-    README.rst
+description = Tempest plugin tests for Cinder.
+long_description = file: README.rst
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
-home_page = http://www.openstack.org/
+url = http://www.openstack.org/
 python_requires = >=3.6
-classifier =
+classifiers =
     Environment :: OpenStack
     Intended Audience :: Information Technology
     Intended Audience :: System Administrators