Split vmlinuz name rather than full path to get version

The ostree-convert-from-debian script is splitting the vmlinuz name to obtain the version and is doing this after concatenating it with the path. This works OK when run with in a docker environment as the path doesn't contain a -, which the script is splitting on. However, if run in the SDK (where we can't use docker) there's a possibility that the path will also contain that character (a strong chance given our recipe repository convention), resulting in the version number being detected completely wrong, enough so to cause images to fail to boot.

Use the vmlinuz name without the path prepended to work out the version.

Signed-off-by: Martyn Welch martyn.welch@collabora.co.uk