Recent openstack cli supports loading user credentials from clouds.yaml
instead of passing each parameters by environment variables or command
options.
This allows us to manage user credentials more flexibly. The biggest
benefit of the clouds.yaml file is that it supports managing multiple
credentials in a single file. When SRBAC is enforced, each API request
should be made with the proper scope credential, and we need to switch
credentials for different scopes(project, domain and system) according.
Usage of clouds.yaml helps this use case hugely because it allows us to
store credentials for each scope in a single file and switch them by
the single OS_CLOUD environment variable(or the --os-cloud option).
Change-Id: Ie8246aa18d90ba506fe708be13c9a5afa3e5d2fd
522d06ba8b