LU-8808 mdt: avoid out of order ChangeLog during restore

LU-8808 mdt: avoid out of order ChangeLog during restore

In hsm_cdt_request_completed(), upon restore completion, layout
lock is returned before associated ChangeLog entry has been created.
This allows for a timing window where concurrent file updater can
take control and create its own ChangeLog out of order (before
restore ChangeLog).
This can puzzle, ChangeLog readers (like RobinHood), and have them
think of a wrong file state.
This patch fixes this hole by posting restore ChangeLog before
giving back layout lock.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I958cb61aab34a6a0edc97f4d1390eed623631c21
Reviewed-on: https://review.whamcloud.com/23638
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>