With directly provide auth string(with contain a json formate
with auth_type and auth info), we can release context to specific
auth_type and give user the ability to provide other Keystone
(or their own) authentication method (like using
`v3applicationcredential` or others).
The format for `auth` and `auth_type` follows exactly Keystone
plugins like in clouds.yaml file [1].
[1] https://docs.openstack.org/keystoneauth/latest/
plugin-options.html#additional-loaders
Change-Id: Ic4dc2292a82860b9bb54ecb9e3b1a4dc806dab2c
Story: #2002126
Task: #26904
4ee754f359