LU-6050 target: control OST-index in IDIF via ROCOMPAT flag

LU-6050 target: control OST-index in IDIF via  ROCOMPAT flag

Introduce new flag OBD_ROCOMPAT_IDX_IN_IDIF that is stored in the
last_rcvd file. For new formatted OST device, it will be auto set;
for the case of upgrading from old OST device, you can enable it
via the lproc interface osd-ldiskfs.index_in_idif. With such flag
enabled, for new created OST-object, its IDIF-in-LMA will contain
the OST-index; for the existing OST-object, the OSD will convert
old format IDIF as new format IDIF with OST-index stored in the
LMA EA when accessing such OST-object or via OI scrub. Once such
flag is enabled, it cannot be reverted back, so the system cannot
be downgraded to the orignal incompatible version.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I9e6e089d54fdb3970bb201eedac8dc09be2cc1c1
Reviewed-on: http://review.whamcloud.com/13516
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>