Add Neutron host-id to RLOC mapping

Add Neutron host-id to RLOC mapping

Neutron port create call provides us informations like port uuid, host-
id, sometimes fixed-ips but we don't know the interface VPP is going to
use for sending traffic from one host to another. That interface is
going to be the locator for the mapping record we will be putting in
the map-cache. For that, we need to know the locator interface of a
host. Just to clarify, for OpenStack environment is going to be the
tenant network interface.

This patch adds the functionality of listening to VbridgeTopology for
topology updates in Virtual Bridge Domain and pre-populate host to
locator information base.

Change-Id: Ic4c0844ccfcb972e46122df875b628c789f8c837
Signed-off-by: Shakib Ahmed <sheikahm@cisco.com>