See if we can upstream our VPN bits to immerda's puppet-tinc module

Originally created by @bertagaz on #11253 (Redmine)

While deploying our monitoring setup, we developed some manifests to handle a Tinc VPN. Immerda has a puppet module for that, but it would need to be adapted to fit our needs. So we should first check if immerda’s module is still maintained, and then check how we could modify so that we can get rid of this lines of code.

Update: https://git.puppet.immerda.ch/module-tinc/ has seen commits in 2018.