LU-1338 hsm: HSM flags feature

LU-1338 hsm: HSM flags feature

This extends lustre_hsm_attrs struct in MDD to store HSM per-file
information. It adds infrastructure (function, RPCs, ...) to read and
modify it, from MDT code or from user-space on clients through llapi
and lfs command.

This patch implements:
- lfs hsm_state
- lfs hsm_set
- lfs hsm_clear

matching llapi functions:
- llapi_hsm_state_get()
- llapi_hsm_state_set()

matching mdt functions:
- mdt_hsm_state_get()
- mdt_hsm_state_set()

and MDS RPC:
- MDS_HSM_STATE_GET
- MDS_HSM_STATE_SET

Signed-off-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Signed-off-by: JC Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: Ic8f82ddc9a56206307c2e5be2523fb7ce42b8638
Reviewed-on: http://review.whamcloud.com/3035
Tested-by: Hudson
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>