LU-11213 ptlrpc: intent_getattr fetches default LMV

LU-11213 ptlrpc: intent_getattr fetches default LMV

Intent_getattr fetches default LMV, and caches it on client,
which will be used in subdir creation.

* Add RMF_DEFAULT_MDT_MD in intent_getattr reply.
* Save default LMV in ll_inode_info->lli_default_lsm_md, and
  replace lli_def_stripe_offset with it.
* take LOOKUP lock on default LMV setting to let client update
  cached default LMV.
* improve mdt_object_striped() to read from bottom device
  to avoid reading stripe FIDs.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Idb369db2c514a9c5108390f70d9284b3a87d26db
Reviewed-on: https://review.whamcloud.com/34802
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>