LU-3083 lmv: swap layout & DNE

If DNE is on, swap layout RPC must be send to the right MDT
and not always to MDT0

Signed-off-by: JC Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: If57ef688c7628bb15a06e1ba6905d3154a204c8d
Reviewed-on: http://review.whamcloud.com/5912
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>