blueprint nec-port-binding
* Add host-id support in port-binding extension.
* Expose portinfo thourgh binding:profile attr in a port.
portinfo is a mapping between neutron port id and OpenFlow switch
physical information (datapath_id and port_no)
It changes the following in portinfo db model
* Add cascade on delete to delete an associated portinfo
when deleting the port.
* Use joined query for portinfo model to retrieve an associated
portinfo when querying a port.
Change-Id: Id88d93dc0770a1290714436324b1b53c0b023eeb
ca30f7712a