LU-1030 clio: reimplement ll_fsync in clio way

LU-1030 clio: reimplement ll_fsync in clio way

A new clio operation CIT_FSYNC is added to forcibly synchorize data
on local client and OST.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: I047471f819c00901907d4312a353095b44dd96a1
Reviewed-on: http://review.whamcloud.com/2460
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>