LU-3834 mdt: handle swap_layouts failures during restore

LU-3834 mdt: handle swap_layouts failures during restore

Actually nothing occur after swap_layouts failures during restore,
this can lead to file being left in incoherent state and thus be
unavailable because HS_RELEASED is clear but LOV_PATTERN_F_RELEASED
is still set.
This patch will allow original layout to be recovered by the use of
SWAP_LAYOUTS_MDS_HSM flag. Additionaly this requires HSM xattr of
the data FID to be set.
Also adds layout-swap failure injection and related test.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Id0e9a005362e4a3854b33f6ce1888197d20e7dbf
Reviewed-on: http://review.whamcloud.com/7631
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>