LU-5584 llite: ensure all data flush out when umount

LU-5584 llite: ensure all data flush out when umount

Write out all extents when clear inode. Otherwise we
may lose data while umount.

Change-Id: I199217c96a7ba49c2f3577a65750e7956a9af63a
Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: http://review.whamcloud.com/12103
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>