Deprecate auth plugins in favour of those from keystoneauth.

Change-Id: I8963ded9b68569717d7a6e30623ee78301b59a4a
Implements: bp deprecate-to-ksa

swap instances of utils.positional with the positional library.

Change-Id: Id8a9961e68d287a802f25512fc970829e9feb5c2

Correct the type signature of some API documentation. Add inter-sphinx
mapping to documentation to provide links to external docs. Correct some
phrases and errors.

Change-Id: Id4a71a9901e5adc695afed656e3bc84e4e54e67a

The argument to the :raises: directive is the class name. If the
class name is a valid reference it's rendered as a link to the
class. This change cleans up the :raises: directives to use the
reference correctly and use a valid class reference.

Change-Id: I84188b60de0ab4c6b5b2fb5a203c43bfde094707

Allow users to specify a default value to loading auth plugins from the
CLI so that you can fallback to some default behaviour if the user
doesn't specify a plugin.

Change-Id: I44eb838f7ccc3b377dd1ba53dbb941e973e4a22e

Split the functions that load the auth plugins from CLI so that they can
be used on a specific plugin. The intention here is to be able to turn
the existing authentication options in shells into a new auth plugin and
have that be loadable rather than maintain separate paths through the
shells.

Change-Id: I3dd5a8ed183d843246b1add3dfbf591ba4e2f94c

With a standard definition of auth plugin options we should be able to
load and use those plugins from command line applications. Provide a
mechanism to register argparse parameters and load from them.

Blueprint: standard-client-params
Change-Id: I5d9904fa885602aaaef7a9e0afd4bd6bbfca3f07