Also fixes a few small docstring syntax errors

Change-Id: I85eb968e32c1191cf5d60d02deff2ab7f3291074

Help for option --os-auth-type doesn't specify what environment variable
configures it. This patch fixes that.

Change-Id: Id2e29e477d5ca56339bd777fb73b5af13788615b

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

* Remove the auth option checks as the auth plugins will validate
  their own options
* Move the initialization of client_manager to the end of
  initialize_app() so it is always called.  Note that no attempts
  to actually authenticate occur until the first use of one of the
  client attributes in client_manager.  This leaves
  initialize_clientmanager() (formerly uathenticate_user()) empty
  so remove it.
* Remove interact() as the client_manager has already been created
  And there is nothing left.
* prepare_to_run_command() is reduced to trigger an authentication
  attempt for the best_effort auth commands, currently the only
  one is 'complete'.
* Add prompt_for_password() to ask the user to enter a password
  when necessary.  Passed to ClientManager in a new kward pw_func.

Bug: 1355838
Change-Id: I9fdec9144c4c84f65aed1cf91ce41fe1895089b2

* Switch to use io.open() for py3 compatibility and simpler testing.
* Open files in 'rb' mode to avoid translation on Windows

Previously tests simply relied on files that were present in the
repository to run tests using open().  Change the filenames to ensure
that no longer happens.

requests_mock doesn't have a way to match against the request body for
PUT/POST; an attempt to add a new Matcher to do that worked but it
needs to subclass the currently private adapter._Matcher class or
duplicate most of its functionality.

Change-Id: I8c30b41db20af8ecafe67e760e872fc08adec905

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>