Port binding enhancement in NEC plugin

This BP covers two features related to port-binding extension.

The one is host-id support in port-binding which is already supported in several plugins.

The other is to expose portinfo in NEC plugin through binding:profile attribute in the port binding extension.
portinfo is a mapping between neutron port id and OpenFlow switch physical information (datapath_id, port number).
This information is usually updated by the plugin agent on compute nodes.
However in cases where baremetal nodes are used or hardware appliance are connected to neutron network, portinfo needs to be registered from outside since there is no plugin agent. Although portinfo needs to be updated from the external system, it is useful to connect hardware nodes to neutron network.