Individual plugin CLI registering

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
Allow registering individual plugin CONF options

Give plugins some more flexibility in registering there own CONF
options.

Change-Id: Id6d47e59e96b7b42c04cecdd53c13a887f60c75b
Merge "Individual plugin CLI registering"
Merge "Allow registering individual plugin CONF options"