remote device communication for dragonflow

This blueprint proposed the solution of communicating to a remote device which is not managed by Dragonflow

Usually we would deploy a VTEP for virtual or physical machine in DC network,
such as the Openvswitch vxlan port, the VTEP TOR(top of rack) and the
physical router which support VTEP, so if Dragonflow knows the correct VTEP
IP, VM in Dragonflow could access remote device by the overlay network.