Report device to engine in a new fashion

Previously we were using the source IP of the socket to the engine
and trying to extract the device out of that.

The new approach is to simulate routing to the engine and get
the device used to forward packets to the engine.

Change-Id: Icedb16c7f0bfccf05ffd2438e013e4894fda20da
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21470
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>