Fix iteration of first-class only models
Fix iteration of first-class only models

Change https://review.openstack.org/#/c/449210/ added indexing of
embedded models and added them to registered models recursively.
In iter_models instead of filtering the registered models by
is_first_class we iterated the whole set and iterated again the embedded
types

Change-Id: I29a995f81fee2507111a00a72ab7970cf2255c60

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow