Add additional openstack client plugins
Add additional openstack client plugins

There are many OpenStack client plugins available now.
(https://github.com/openstack/python-openstackclient/blob/master/doc/source/commands.rst#plugin-objects)

Update the generation script to include a more up to date list.

This is related to the work for the bp below.
Blueprint: heat-support-python-openstackclient

Change-Id: I0b41bc72cf597fe6e9ba27c1d07005567594bfd1

openstack/openstack-doc-tools,openstack/openstack-doc-tools