Add a container_manager validation (#8785)

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

@@ -217,6 +217,12 @@
   when:
     - inventory_hostname in groups.get('etcd',[])
 
+- name: Stop if container manager is not docker, crio or containerd
+  assert:
+    that: container_manager in ['docker', 'crio', 'containerd']
+    msg: "The container manager, 'container_manager', must be docker, crio or containerd"
+  run_once: true
+
 - name: Stop if etcd deployment type is not host or kubeadm when container_manager != docker
   assert:
     that: etcd_deployment_type in ['host', 'kubeadm']