LU-2213 scrub: stop LFSCK before osd_shutdown

LU-2213 scrub: stop LFSCK before osd_shutdown

The osd_shutdown will clean all the otable-based iteration,
but up layer LFSCK depends on the otable-based iteration.

So we need to stop the LFSCK before osd_shutdown called.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I97625d54766122314630aff0069d9e14d23b9840
Reviewed-on: http://review.whamcloud.com/4217
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>