LU-9771 flr: instantiate component for truncate

LU-9771 flr: instantiate component for truncate

layout intent for truncate IO needs stale components for non
primary mirror overlapping [trunc_size, eof), while needs to
instantiate components overlapping [0, trunc_size).

Test-Parameters: testlist=sanity-flr
Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: Ibf31e3e1fd68d1a643f2ed3ac5b9e3c778563895
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: https://review.whamcloud.com/29099
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>