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: I74130dab437c7ec7333d19bf2efc6f9b6095a0ff

setup.cfg

@@ -1,11 +1,11 @@
 [metadata]
 name = ansible-config_template
 summary = Config Template plugin for Ansible
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = https://docs.openstack.org/ansible-config_template/latest/
+author_email = openstack-discuss@lists.openstack.org
+home_page = https://docs.openstack.org/ansible-config_template/latest/
 classifier =
     Intended Audience :: Developers
     Intended Audience :: System Administrators
@@ -14,8 +14,8 @@ classifier =
 
 [build_sphinx]
 all_files = 1
-build-dir = doc/build
-source-dir = doc/source
+build_dir = doc/build
+source_dir = doc/source
 
 [pbr]
 skip_authors = True
@@ -25,7 +25,7 @@ skip_changelog = True
 universal = 1
 
 [global]
-setup-hooks =
+setup_hooks =
     pbr.hooks.setup_hook
 
 [files]