LU-2775 osp: enable fid-on-OST only for DNE.

1. MDT0 will only create IDIF fids, so old clients, who
only know IDIF, can still access files on MDT0.

2. Using fid_ostid_pack to pack the FID into ostid, otherwise
IDIF will be packed wrongly and caused the panic on the OST0.

3. Add dd into compatible tests of conf-sanity.sh(32) to
check OST fids on the upgrade FS.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ic9322bd1c66e5fedec68c10aa2f300d5ecb3b6db
Reviewed-on: http://review.whamcloud.com/5307
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>