LU-10383 hsm: consolidate CDT restore handle handling

LU-10383 hsm: consolidate CDT restore handle handling

Consolidate duplicated HSM coordinator restore handle handling into
new functions cdt_restore_handle_{add,del_(). Rename
mdt_hsm_restore_hdl_find() and some struct members for consistency.

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I9798ed93ea26a9d61d4786540c6dae95cdc38c4b
Reviewed-on: https://review.whamcloud.com/30557
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>