Openflow (events) Extensions for Openstack OVS-Agent and corresponding ML2-Plugin Mechanism Driver.

The goal of this work is to add Openflow (events) extensions to the openstack's ovs-agent and develop corresponding ML2-plugin mechnism driver. The extensions for ovs-agent should be as loosely-coupled as possible. This extension can be a 'stripped-down' version of an openflow-controller. This work tries to address the following two goals:
1. Effectively utilization of Openflow in compute-nodes: The power of openflow should be well utilized by the OVS agent in compute-nodes. 2. Using openflow-events to ensure achieve Neutron database consistency management: If any failures in the virtual-bridges, and/or the physical interfaces/ports, the neutron database-consistency may be affected. The goal is to take advantage of openflow-events.