LU-14459 mdt: restripe parent may be a stripe

LU-14459 mdt: restripe parent may be a stripe

mdt_restripe() check parent LMV sanity with lmv_is_sane(), but parent
may be a stripe, use lmv_is_sane2() instead.

Clear lmv_migrate_hash/offset in layout shrink/update, though it
won't cause any issue, it's strange to see values set in debug logs.

Add more race check between directory restripe, auto-split and
migration.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I38950a07a8c9a8b4b20a2fd7aff229d27dbb403c
Reviewed-on: https://review.whamcloud.com/43290
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>