LU-2886 scrub: non-fixed FIDs for some local files

For old lustre-2.x (x < 4), the local files PENDING/lfsck_bookmark
used fixed/reserved FIDs when created. The cases have been changed
to use variable local FIDs since lustre-2.4. So adjust OI scrub to
match the changes.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I6d1f2f19afa3d777b16838ae03f46a39a58b537a
Reviewed-on: http://review.whamcloud.com/6299
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>