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

roles/kubernetes/preinstall/tasks/0040-set_facts.yml

roles/kubernetes/preinstall/tasks/0060-resolvconf.yml

roles/kubernetes/preinstall/tasks/0070-system-packages.yml

...ubernetes/preinstall/tasks/0080-system-configurations.yml

roles/kubernetes/preinstall/tasks/main.yml

roles/kubespray-defaults/defaults/main.yaml

roles/network_plugin/macvlan/handlers/main.yml

roles/network_plugin/macvlan/tasks/main.yml

roles/reset/tasks/main.yml

tests/testcases/015_check-pods-running.yml

tests/testcases/030_check-network.yml

tests/testcases/040_check-network-adv.yml