LU-2061 hsm: get list of HSM actions

LU-2061 hsm: get list of HSM actions

This patch implements a MDS RPC to get
the list of registered and running hsm actions on files

It implements:
- lfs hsm_action

The matching llapi call:
- llapi_hsm_current_action()

The matching MDS function:
- mdt_hsm_action()

and MDS RPC:
- MDS_HSM_ACTION

Signed-off-by: JC Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: If4b00949ca8c94c8572cc81a7f7b8db32914542c
Reviewed-on: http://review.whamcloud.com/5029
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>