Address standalone kubelet config case

Also place in global vars and do not repeat the kube_*_config_dir
and kube_namespace vars for better code maintainability and UX.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

roles/kubernetes-apps/ansible/templates/kubedns-svc.yml

@@ -2,7 +2,7 @@ apiVersion: v1
 kind: Service
 metadata:
   name: kubedns
-  namespace: {{ kube_namespace }}
+  namespace: {{ system_namespace }}
   labels:
     k8s-app: kubedns
     kubernetes.io/cluster-service: "true"