LU-2888 osd: OI implemented within OSD

This patch is mostly port of master commit f2f09b6e, which uses
ldiskfs directly to implement OI, so that be align with 2.4 lustre.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: If83cd61b6c90e195a7a364153819bbec8aa0f9c1
Reviewed-on: http://review.whamcloud.com/5731
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>