LU-4198 clio: generalize cl_sync_io

To make cl_sync_io interfaces not just wait for pages, but to be
a generic synchronization mechanism.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Iea43cb56c463efa7a6c6d17d84dacf4bdad8b377
Reviewed-on: http://review.whamcloud.com/8656
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Jenkins
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>