I suppose that methods get_resource_manager_extra_kwargs and
add_resource_manager_extra_kwargs_hook were designed in those days when
Nova API had extensions.
Nowdays, Nova API has strict schema validation of requests, so no
additional arguments are allowed and these methods look redundant.
The fact that get_resource_manager_extra_kwargs lists of the objects
added by add_resource_manager_extra_kwargs_hook whereas
add_resource_manager_extra_kwargs_hook is not called anywhere
doesn't add chances for leaving these methods in our code.
Compatibility: both methods are designed for CLI and the CLI behaviour
will not change after removing them, so we can do a cleanup without
following standard deprecation cycle.
Change-Id: Id61457c3db8a17e2294dc579b2519873927fec48
ca27736810