Add image builder to create Docker vm's for kube-virt

test-infra/image-builder/Makefile

test-infra/image-builder/cluster.yml

test-infra/image-builder/hosts.ini

...fra/image-builder/roles/kubevirt-images/defaults/main.yml

...-infra/image-builder/roles/kubevirt-images/tasks/main.yml

.../image-builder/roles/kubevirt-images/templates/Dockerfile