LU-13635 lfs: add -D option back to lfs_migrate

LU-13635 lfs: add -D option back to lfs_migrate

Enable "-D" option with its long option "--non-direct" correctly
in lfs_migrate.
sanity.sh test_56we is added to verify this patch.

Test-Parameters: trivial
Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I6ab051c0f2e0cde9de6a5b8ace8962cc293e7656
Reviewed-on: https://review.whamcloud.com/38840
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>