LU-5666 llapi: LLAPI helpers for group lock.

LU-5666 llapi: LLAPI helpers for group lock.

Introduced llapi_group_{lock,unlock} functions to abstract the ioctl
implementation to manipulate group lock. Updated lfs accordingly.

Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Change-Id: I9c0c75029cd0d159e353a2c925cecc9b4ba9a6de
Reviewed-on: http://review.whamcloud.com/12053
Tested-by: Jenkins
Reviewed-by: frank zago <fzago@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>