LU-13425 lfs: support numeric hash type by "lfs migrate -H"

LU-13425 lfs: support numeric hash type by "lfs migrate -H"

This patch allows "lfs migrate -H" to use numertic hash type in case
of any error message returned by the server in such a form, e.g.
"run 'lfs migrate -m 1 -c 1 -H 3 dir1' to finish migration".

sanity.sh test_230d is modifed a little to verify this patch and
lfs-migrate.1 and lfs migrate usage is updated to reflect this change.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I19cda608b2d28e8e392f03db366767b829ed6dc6
Reviewed-on: https://review.whamcloud.com/38182
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>