LU-3590 lfsck: repair MDT-object with dangling reference

LU-3590 lfsck: repair MDT-object with dangling reference

If the OST-object referenced by the MDT-object is lost, then the
LFSCK needs to recreate the OST-object with the specified FID and
initialize it with the given parent MDT-object FID and owner attr.
Although the new created OST-object is initialized, the SUID+SGID
mode will be kept, which will be dropped by the first modification
RPC, like write/punch/setattr. Then we can distinguish whether the
recreate OST-object has been modified or not.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ic45254695e7b1902020c133bb23fd32685b9a414
Reviewed-on: http://review.whamcloud.com/7517
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>