use openflow controller plugin to omit openvswitch-agent and l3-agent

Use some openflow-plugins to config openflow switchs (physical openflow-switch or openvswitch without agents) directly in order to omit the agents(like neutron-plugin-openvswitch-agent and neutron-l3-agent) in the network node and compute node, providing easier and more flexible network deployments and making the development of new network function easier. The network functions of network node are implemented only by openflow switchs(without linux protocol stack)