Improved Ubuntu repository add

The driving factor behind these changes is to add flexibility to the TDL format for apt (like yum has) and ensure that we are writing out to `sources.list.d` instead of only using `add-apt-repository`. `add-apt-repository` will write everything except PPAs and cloud-archive's to sources.list; those 2 get written to `sources.list.d` directory. `cloud-init` has an option to inject (and thus overwrite) all default mirrors in `/etc/apt/sources.list`.

This causes any additional repos oz adds to get blown away.