Python client examples don't work

[John Griffith]

We have some handy documentation on how to use the cinderclient directly from python, but unfortunately said documentation is out of date and doesn't work [1].

In the case of creating a session, Keystone requires that the the OS_USER_DOMAIN_ID is supplied, so we should update the docs to reflect that appropriately.

As far as direct instantiation of the client I'm not sure what's wrong with that yet, but the result thus far is a "requires authorization" exception when trying to issue any requests.

[1]: https://docs.openstack.org/python-cinderclient/latest/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/555373

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/555373
Committed: https://git.openstack.org/cgit/openstack/python-cinderclient/commit/?id=d6c6011fc83ab9a3bbd65e8dd4557ebf25b363ae
Submitter: Zuul
Branch: master

commit d6c6011fc83ab9a3bbd65e8dd4557ebf25b363ae
Author: j-griffith <email address hidden>
Date: Thu Mar 22 10:50:51 2018 -0600

    Update python usage docs

    The keystoneauth1 get_plugin_loader method requires that a
    OS_USER_DOMAIN be specified. Our docs don't include that
    detail.

    This change adds the extra needed field. There's also some
    problems currently with loading the client directly as it's
    currently documented, which appears to be a bug in the client
    code itself.

    Change-Id: Idacbb47f9aae1e461379eec4a5e224b0157a8dc4
    Partial-Bug: #1758104