Fix assertion for alone etcd nodes (#3847)

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

@@ -108,7 +108,7 @@
 - name: Stop if RBAC and anonymous-auth are not enabled when insecure port is disabled
   assert:
     that: rbac_enabled and kube_api_anonymous_auth
-  when: kube_apiserver_insecure_port == 0
+  when: kube_apiserver_insecure_port == 0 and inventory_hostname in groups['kube-master']
   ignore_errors: "{{ ignore_assert_errors }}"
 
 - name: Stop if kernel version is too low