Comment 1 for bug 1293738

We could add a new tag like 'solum::lp::hash' which can be a MD5 value calculated from other important tag values, e.g. 'type', 'os_platform', 'compiler_version' etc.. When creating a new language pack, we can first query the database to check if there is already an image with a same hash. We need to update the hash whenever we update the tag values via a PUT.