I can't remember right now why I needed to use Debian's MariaDB build
but now I just want to use upstream's latest stable. Debian's version
is 10.1 and upstream has moved on to 10.2.
When I originally deployed Ubuntu 16.04 there were no public xenial
MariaDB builds yet, so I used wily (15.10). Now there are official
xenial builds so we can use them instead.
When you use the apt_repository module it adds a sources.list with
an annoying filename, and also it's just easier to use a template
when we have different distros/versions to support.
