LU-9771 ptlrpc: use lu_extent in layout_intent

LU-9771 ptlrpc: use lu_extent in layout_intent

This way it will be easier to check and print the extent
of layout.

Test-Parameters: testlist=sanity-flr

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ie99142388310a8e321899c1795bc16bee97657be
Reviewed-on: https://review.whamcloud.com/29087
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>