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-apps/network_plugin/weave/tasks/main.yml

@@ -5,7 +5,7 @@
     kubectl: "{{ bin_dir }}/kubectl"
     filename: "{{ kube_config_dir }}/weave-net.yml"
     resource: "ds"
-    namespace: "{{system_namespace}}"
+    namespace: "kube-system"
     state: "latest"
   when: inventory_hostname == groups['kube-master'][0]