LU-4525 lfsck: distinguish objects visibility by LFSCK

Originally, the ldiskfs backend otable-based iteration only returned
namespace visible FIDs. That means that the OSD needs to distinguish
related objects visibility. But the OSD should not has the knowledge
about the objects visibility. It is the iteration caller - LFSCK, to
distinguish that by itself.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I1eef4041170e856af00a4b222d053ccb3d8d0023
Reviewed-on: http://review.whamcloud.com/9186
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>