Puppet doesn't support variable reassignment, so using concat() from
the puppetlabs/stdlib seems to be easier than making up a series of
arbitrary variable names.
Puppet removed the "+=" and "-=" operators. Replaced with $a = $a +
$b, which requires Puppet 4.x. If compatibility with 3.x is desired,
the code needs to be changed to use an external function, like concat().
Kienan Stewart