LU-4640 mdt: implement Remove Archive on Last Unlink policy

LU-4640 mdt: implement Remove Archive on Last Unlink policy

This reverts commit d9f95aa201341d972eeb610471e3c45f1ba12202 which
had already reverted original commit
74d92933108dc64b110a843352cf3336dca249d0 for LU-4640, to rebase
and re-integrate original patch changes.

In addition, necessary changes (LU-7881) have been added to make
sanity-hsm/test_26b comply with LU-7136 recent changes in
sanity-hsm internal framework/functions. And also to comply with
concurrent changes that had caused object to become unavailable
earlier than expected in original patch version, by moving
mdt_handle_last_unlink() call in mdt_mfd_close() now.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I172d778dad494d36a6f5d03e261b2ba584fb6542
Reviewed-on: https://review.whamcloud.com/18946
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>