complete processing for plugin calls

[Robert Kukura]

When policy drivers invoke plugin methods to create or manipulate GBP or neutron resources, not all the functionality is performed occurs when those same methods are called via the REST API. Start and end notifications are not sent, quotas aren't enforced, and API authorization is not checked. We need to determine which of these are needed and implement them. See the REVISIT comments in the _create_resource, _update_resource, and _delete_resource methods in gbp/neutron/services/grouppolicy/drivers/resource_mapping.py.