LU-3647 hsm: Add support to drop all pages for ll_data_version

LU-3647 hsm: Add support to drop all pages for ll_data_version

This will be used by HSM release to get data version and drop all
caching pages from all clients, before sending IT_RELEASE close
REQ to MDT.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I670521881d77dfa584e9124d21eb65b048cc82e9
Reviewed-on: http://review.whamcloud.com/6794
Tested-by: Hudson
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>