Stop templating kube-system namespace and creating it (#2545)

Kubernetes makes this namespace automatically, so there is
no need for kubespray to manage it.

roles/kubernetes/node/templates/manifests/kube-proxy.manifest.j2

@@ -2,7 +2,7 @@ apiVersion: v1
 kind: Pod
 metadata:
   name: kube-proxy
-  namespace: {{system_namespace}}
+  namespace: kube-system
   labels:
     k8s-app: kube-proxy
   annotations:

roles/kubernetes/node/templates/manifests/nginx-proxy.manifest.j2

@@ -2,7 +2,7 @@ apiVersion: v1
 kind: Pod
 metadata:
   name: nginx-proxy
-  namespace: {{system_namespace}}
+  namespace: kube-system
   labels:
     k8s-app: kube-nginx
 spec: