Fix route operation errors.
Fix a typo of 'routes' not 'routers'
Change 'external_gateway_info' and 'routes' declarations.
Change 'ip_version' and 'host_routes' handling to avoid subnet operation errors.
Make PortForCreate Serializable.
Add version 2.0 as the top element of resource paths(netowks/subnets/routers/ports).