This patch adds an agent extension for Neutron
openvswitch agent to make the metadata
datapath distributed.
The extension will do the following works when
handle port:
1. allocate Meta_IP and Meta_MAC
2. setup the host haproxy configurations for this port
3. cache port infos for deleting
The extension will do the following works when
delete port:
1. remove haproxy configurations of this port
2. clean up cache infos
Partially-Implements: blueprint distributed-metadata-datapath
Change-Id: Ia6e3e57b7e2ff61e8e7c950c095df15ffa3abd7a