added "Flatcar", "Flatcar Container Linux by Kinvolk" for all coreOS role (#5607)

contrib/vault/roles/vault/tasks/bootstrap/ca_trust.yml

roles/bootstrap-os/tasks/bootstrap-coreos.yml

roles/bootstrap-os/tasks/main.yml

roles/container-engine/docker/handlers/main.yml

roles/container-engine/docker/tasks/main.yml

roles/container-engine/docker/tasks/systemd.yml

roles/download/defaults/main.yml

roles/download/tasks/download_container.yml

roles/download/tasks/download_file.yml

roles/download/tasks/prep_download.yml

roles/download/tasks/sync_container.yml

roles/download/tasks/sync_file.yml

roles/etcd/meta/main.yml

roles/etcd/tasks/upd_ca_trust.yml

...s/external_provisioner/local_volume_provisioner/README.md

roles/kubernetes-apps/helm/tasks/install_host.yml

roles/kubernetes-apps/helm/tasks/main.yml

roles/kubernetes/node/tasks/install.yml

roles/kubernetes/preinstall/handlers/main.yml

roles/kubernetes/preinstall/tasks/0020-verify-settings.yml