BindingXMLRPC bugfix: Use getDeviceByIP() for lastClientIface

Use the new function introduced in:
http://gerrit.ovirt.org/#/c/22841/

To report the 'management device' to the engine.

Change-Id: Ic17e91c80560cd3acb73e7a64879257a6e07b1fe
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22842
Reviewed-by: Dan Kenigsberg <danken@redhat.com>