4 images: ['waffleimage/debian8']
7 images: ['debian:8', 'debian:9', 'ubuntu:16.04', 'ubuntu:18.04']
10 images: ['waffleimage/debian8', 'waffleimage/debian9', 'waffleimage/ubuntu16.04', 'waffleimage/ubuntu18.04']
13 images: ['centos/7', 'generic/ubuntu1804']
16 images: ['debian-8-x86_64', 'debian-9-x86_64', 'debian-10-x86_64', 'ubuntu-1604-x86_64', 'ubuntu-1804-x86_64']