python-openstackclient, shade, openstacksdk and Ansible's OpenStack
modules all support reading client config information from a file called
clouds.yaml instead of from environment variables set from openrc files.
Unfortunately, the only thing horizon currently offers for download is
old-style openrc files.
Add support for downloading clouds.yaml files.
Change-Id: I0611dd44524b746ad993bff7435ec8628a83a762