LU-13683 lfs: return -ENOENT when invoked on non-existing file

LU-13683 lfs: return -ENOENT when invoked on non-existing file

Since merge of LU-11510, lfs migrate on a non-existing file will give
the following error "lfs migrate: can't create composite layout from
file /some/path/to/file" and will exit with code 0, potentially
leaving a calling script unaware of the error.

This patch fixes it by using errno which is set in the call to
llapi_layout_get_by_path()

Signed-off-by: Sebastien Piechurski <sebastien.piechurski@atos.net>
Change-Id: I910eae78445f6071ff4e741afd43d140f554ab22
Fixes: 8bedfa377fbd ("LU-11510 lfs: migrate a composite layout file correctly")
Reviewed-on: https://review.whamcloud.com/38953
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>