update to safeguard against accidentally passing string instead of list

roles/kubernetes/master/templates/manifests/kube-apiserver.manifest.j2

@@ -81,9 +81,13 @@ spec:
 {% if kube_api_anonymous_auth is defined and kube_version | version_compare('v1.5', '>=')  %}
     - --anonymous-auth={{ kube_api_anonymous_auth }}
 {% endif %}
+{% if apiserver_custom_flags is string %}
+    - {{ apiserver_custom_flags }}
+{% else % }
 {%   for flag in apiserver_custom_flags %}
     - {{ flag }}
 {%   endfor %}
+{% endif %}
     livenessProbe:
       httpGet:
         host: 127.0.0.1

roles/kubernetes/master/templates/manifests/kube-controller-manager.manifest.j2

@@ -46,9 +46,13 @@ spec:
     - --configure-cloud-routes=true
     - --cluster-cidr={{ kube_pods_subnet }}
 {% endif %}
+{% if controller_mgr_custom_flags is string %}
+    - {{ controller_mgr_custom_flags }}
+{% else % }
 {%   for flag in controller_mgr_custom_flags %}
     - {{ flag }}
 {%   endfor %}
+{% endif %}
     livenessProbe:
       httpGet:
         host: 127.0.0.1

roles/kubernetes/master/templates/manifests/kube-scheduler.manifest.j2

@@ -27,9 +27,13 @@ spec:
     - --leader-elect=true
     - --master={{ kube_apiserver_endpoint }}
     - --v={{ kube_log_level }}
+{% if scheduler_custom_flags is string %}
+    - {{ scheduler_custom_flags }}
+{% else % }
 {%   for flag in scheduler_custom_flags %}
     - {{ flag }}
 {%   endfor %}
+{% endif %}
     livenessProbe:
       httpGet:
         host: 127.0.0.1

roles/kubernetes/node/templates/kubelet.j2

@@ -44,7 +44,7 @@ KUBELET_HOSTNAME="--hostname-override={{ ansible_hostname }}"
 {%   set node_labels %}--node-labels=node-role.kubernetes.io/node=true{% endset %}
 {% endif %}
 
-KUBELET_ARGS="{{ kubelet_args_base }} {{ kubelet_args_dns }} {{ kubelet_args_kubeconfig }} {{ node_labels }} {% for flag in kubelet_custom_flags %} {{flag}} {% endfor %}"
+KUBELET_ARGS="{{ kubelet_args_base }} {{ kubelet_args_dns }} {{ kubelet_args_kubeconfig }} {{ node_labels }} {% if kubelet_custom_flags is string %}{{kubelet_custom_flags}}{% else %}{% for flag in kubelet_custom_flags %} {{flag}} {% endfor %}{% endif %}"
 {% if kube_network_plugin is defined and kube_network_plugin in ["calico", "weave", "canal"] %}
 KUBELET_NETWORK_PLUGIN="--network-plugin=cni --network-plugin-dir=/etc/cni/net.d --cni-bin-dir=/opt/cni/bin"
 {% elif kube_network_plugin is defined and kube_network_plugin == "weave" %}