LU-14459 lmv: change default hash type to crush

LU-14459 lmv: change default hash type to crush

Change the default hash type to CRUSH to minimize the number
of directory entries that need to be migrated.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I75aff45898044be9d12ae1bfad31b4693b3ebbe5
Reviewed-on: https://review.whamcloud.com/43684
Reviewed-by: Lai Siyao <lai.siyao@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>