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: I831f08154dad5a80e8f34aeb9ae161d2de5ffa57

setup.cfg

 [metadata]
 name = kayobe
 summary = Deployment of OpenStack to bare metal using OpenStack kolla and bifrost
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
-home-page = https://docs.openstack.org/kayobe/latest/
-python-requires = >=3.6
+author_email = openstack-discuss@lists.openstack.org
+home_page = https://docs.openstack.org/kayobe/latest/
+python_requires = >=3.6
 license = Apache License, Version 2.0
 classifier =
     Environment :: OpenStack