LU-10565 osd: unify interface for vfs

LU-10565 osd: unify interface for vfs

Some vfs changes were applied to other part but
OSD. So unify them with OSD layer.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: Ia3e907964d6321571f52e4c24a46a8ab64e4d056
Reviewed-on: https://review.whamcloud.com/31646
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>