LU-5523 mdt: add --index option to default dir stripe

LU-5523 mdt: add --index option to default dir stripe

Add --index option to default dirstripe EA. If MDT find
out the client send the create req to the wrong MDT because
of default stripeEA, it will return -EREMOTE, then client
will retrieve default stripeEA through xattr cache, and
re-create the object.

Add delete default dirstripeEA (-d) to delete dir default
stripeEA.

Add ldo_dir_def_striping_cached and ldo_def_striping_cached
to means if default striping EA has been cached in ldo_object.

And ldo_striping_cached means if the object's own striping
has been loaded from disk.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ic2896e9050f1581344db9368b8f7b25bfded3d7d
Reviewed-on: http://review.whamcloud.com/13360
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>