Lint the things

Back in my days of ansible + infrastructure operations, I used the following alias to help ensure that all my yaml files followed a consistent pattern. I used this to lint all of your yaml files which in turn fixed a few things. I added the yamllint to your gitlab-ci file so that everyone can benefit. I updated your Makefile to take advantage of make's features such as sourcing targets to cut down on repetitive code.

alias yams='find . -type f -name "*.yml*" | sed "s|\./||g" | egrep -v "(\.kitchen/|\[warning\]|\.molecule/)" | xargs yamllint -f parsable'

This is a sweet project.