User's don't know what a plugin is.

* Internally, os_auth_type and/or auth_type represents what the
  user supplied.
* auth_plugin_name is the name of the selected plugin
* auth_plugin is the actual plugin object

Plugin selection process:
* if --os-auth-type is supplied:
  * if it matches against an available plugin, done
  * (if it can map to an availble plugin type, done; TODO in a followup)
* if --os-auth-type is not supplied:
  * if --os-url and --os-token are supplied, select 'token_endpoint'
  * if --os-username supplied, select identity_api_version + 'password'
  * if --os-token supplied, select identity_api_version + 'token'

Change-Id: Ice4535214e311ebf924087cf77f6d84d76f5f3ee

Anything that needs a service catalog can get it directly from
auth_ref.service_catalog, no need to carry the extra attribute.

ClientManager.get_endpoint_for_service_type() reamins the proper
method to get an endpoint for clients that still need one directly.

Change-Id: I809091c9c71d08f29606d7fd8b500898ff2cb8ae

Clients that can use ksc Session don't need the old junk to
fake auth anymore:
* compute
* volume

Clients that still need to be fed credentials can pick directly
from the auth object in clientmanager.  The _token attribute is
removed, the token can be retrieved from the auth object:

  openstackclient/tests/common/test_clientmanager.py

This change will break any plugin that relies on getting a token
from instance._token. They should be updated to use the above, or
preferable, to use keystoneclient.session.Session to create its
HTTP interface object.

Change-Id: I877a29de97a42f85f12a14c274fc003e6fba5135

keystoneclient/openstack/common/jsonutils.py is removed in this patch
https://review.openstack.org/#/c/128454/
Now, we should use jsonutils in oslo.serialization package.

Change-Id: I7c8e8e6d5dffa85244368fd578616c9b19f4fd21

The ksc auth plugins do not have support for the original
token-endpoint (aka token flow) auth where the user supplies
a token (possibly the Keystone admin_token) and an API endpoint.
This is used for bootstrapping Keystone but also has other uses
when a scoped user token is provided.

The api.auth:TokenEndpoint class is required to provide the
same interface methods so all of the special-case code branches
to support token-endpoint can be removed.

Some additional cleanups related to ClientManager and creating
the Compute client also were done to streamline using sessions.

Change-Id: I1a6059afa845a591eff92567ca346c09010a93af

This patch allows the user to choose which authentication plugin
to use with the CLI. The arguments needed by the auth plugins are
automatically added to the argument parser. Some examples with
the currently available authentication plugins::

  OS_USERNAME=admin OS_PROJECT_NAME=admin OS_AUTH_URL=http://keystone:5000/v2.0 \
  OS_PASSWORD=admin openstack user list

  OS_USERNAME=admin OS_PROJECT_DOMAIN_NAME=default OS_USER_DOMAIN_NAME=default \
  OS_PROJECT_NAME=admin OS_AUTH_URL=http://keystone:5000/v3 OS_PASSWORD=admin \
  OS_IDENTITY_API_VERSION=3 OS_AUTH_PLUGIN=v3password openstack project list

  OS_TOKEN=1234 OS_URL=http://service_url:35357/v2.0 \
  OS_IDENTITY_API_VERSION=2.0 openstack user list

The --os-auth-plugin option can be omitted; if so the CLI will attempt to
guess which plugin to use from the other options.

Change-Id: I330c20ddb8d96b3a4287c68b57c36c4a0f869669
Co-Authored-By: Florent Flament <florent.flament-ext@cloudwatt.com>

* Add method to CommandManager to retrieve command names by group
* Add ListCommands

To list command groups loaded by cliff

Change-Id: I37fe2471aa2fafa8aa223159452d52b1981021d6

Cliff 1.6.1 added  CommandManager.load_commands() so we can adopt it
rather than rolling our own.

Also, that second group is Greek, not Latin.  Jeez...

Change-Id: I4a63c22f37bcfd0ef5d83c2dbd08b58fda0db35c