Introduce dns_mode and resolvconf_mode and implement docker_dns mode

.gitlab-ci.yml

cluster.yml

contrib/terraform/openstack/group_vars/all.yml

docs/dns-stack.md

docs/figures/dns.jpeg

inventory/group_vars/all.yml

roles/dnsmasq/defaults/main.yml

roles/dnsmasq/meta/main.yml

roles/docker/tasks/main.yml

roles/docker/tasks/set_facts_dns.yml

roles/docker/tasks/systemd.yml

roles/docker/templates/docker-dns.conf.j2

roles/docker/templates/docker.service.j2

roles/kubernetes-apps/ansible/tasks/main.yaml

roles/kubernetes/node/templates/kubelet.j2

roles/kubernetes/preinstall/tasks/main.yml

roles/kubernetes/preinstall/tasks/set_resolv_facts.yml

roles/reset/tasks/main.yml