LU-3335 scrub: control OI scrub on OST from user space

LU-3335 scrub: control OI scrub on OST from user space

Not all the OI inconsistency can be detected automatically, such as /O
entry lost case. So the OI scrub on OST should can be triggered by the
administrator manually.

Test-Parameters: testlist=sanity-scrub
Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I9b23787b2fb14c8c93642462f9ebac948a181b70
Reviewed-on: http://review.whamcloud.com/6698
Tested-by: Hudson
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>