Remove rkt support (#4671)

roles/etcd/templates/etcd-events-rkt.service.j2

roles/etcd/templates/etcd-rkt.service.j2

...ernetes/kubeadm/templates/kubeadm-client.conf.v1alpha2.j2

...ernetes/kubeadm/templates/kubeadm-client.conf.v1alpha3.j2

...bernetes/kubeadm/templates/kubeadm-client.conf.v1beta1.j2

...bernetes/master/templates/kubeadm-config.v1alpha2.yaml.j2

...bernetes/master/templates/kubeadm-config.v1alpha3.yaml.j2

...ubernetes/master/templates/kubeadm-config.v1beta1.yaml.j2

...tes/master/templates/kubeadm-controlplane.v1beta1.yaml.j2

roles/reset/tasks/main.yml

tests/files/gce_ubuntu-rkt-sep.yml

tests/files/packet_ubuntu-rkt-sep.yml