clouds.yaml[0] is a richer way to express configuration for OpenStack
clouds. It's also fully supported by Ansible's OpenStack modules as
well as python-openstackclient and openstacksdk. It's the future - who
doesn't like the future?

Write a file using both the public (default) and the internal endpoints
for the admin user. Also, change all of the examples to reference it
and to get python-openstackclient to use it too.

[0] https://docs.openstack.org/openstacksdk/latest/user/guides/connect_from_config.html

Implements: blueprint use-clouds-yaml
Change-Id: I557d2e4975c7b3d3c713a556b9ba47af9567ce6e