LU-8626 hsm: expose the number of active hsm requests per type

LU-8626 hsm: expose the number of active hsm requests per type

This patch creates 3 new proc files under the hsm directory:
 - archive_count
 - restore_count
 - remove_count

These should help monitor the coordinator's health and allow
policy engine to adapt their request flow.

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: Quentin Bouget <quentin.bouget@cea.fr>
Change-Id: I30c9fb658e8c14a181b094b51408c92df609c3ca
Reviewed-on: https://review.whamcloud.com/30336
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Stephan Thiell <sthiell@stanford.edu>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>