Moving the repo_data logic into the utils.blender function

This makes the repo data available to any template function that
calls blender (which is most of them) as opposed to having to copy
the logic into each individual function
Adding a snippet to rewrite sources.list for debian/ubuntu

So that there's a nice clean file without a lot of extraneous
entries, plus a fix to the preseed_apt_repo_config for repos that
are not mirrored locally (incorrect url formatting)