Pub/Sub Refactor for DragonFlow

Currently not all the applications work for pub/sub layer, because some applications require df-local-controller to be publisher, some refactor work needs to be done to make pub/sub more flexible.

Keep DB Consistency between Neutron and Dragonflow for DragonFlow

Currently, there's inconsistency between Neutron DB and Dragonflow DB, especially in multi-nodes deployment. We need to make sure all the DB operations are synced. Otherwise, it cannot be ready for production.

Full support of ZeroMQ driver for devstack

1. Background The oslo team has reached an agreement during Paris design summit that we will continuely support ZeroMQ driver. Due to its distributed nature, ZeroMQ can scale out very well. All the bug fixes have been proposed and most of them have been fixed and merged to upstream. The biggest problem of using Ze...