SDK Refactor: Prepare network rbac commands
SDK Refactor: Prepare network rbac commands

Prepare the OSC "network rbac" commands for the SDK refactor.
See [1] for details.

[1] https://etherpad.openstack.org/p/osc-network-command-sdk-support

Change-Id: I6f25e167d7f933667173b04a4b0ad55baf3c56f2
Partially-Implements: blueprint network-command-sdk-support

openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,dtroyer/python-openstackclient