Subport: Ping failed after cluster reboot

Subport: Ping failed after cluster reboot

With cluster reboot, subport interfaces some times gets created as Trunk
interfaces. This is mainly because of port and trunk replay executing in
irregular order after reboot sometimes.

Below changes are done to fix above problem:
(a) New yang container as shown below is introduced to save subport details
needed for creating subport-interface in CONFIG DS (this is defined in neutronvpn.yang)

    container neutron-vpn-port-id-subport-data {
        config true;
        list port-id-to-subport {
            key port-id;
            leaf port-id { type yang:uuid; }
            leaf vlan-id { type uint32; }
            leaf trunk-port-id { type yang:uuid; }
        }
    }

(b) After cluster restart, get details about subport from config DS using neutron port id.
If data is present, create interface as subport interface (trunk-member) otherwise create
it as trunk interface.

Change-Id: I8a7baf868ef51c1f8264d79020564e2e89207bfa
Signed-off-by: Shashidhar Raja <shashidharr@altencalsoftlabs.com>