Bind nginx localhost proxy to localhost

This proxy should only be listening for local connections, not 0.0.0.0.

Fixes #868

roles/kubernetes/node/templates/nginx.conf.j2

@@ -16,7 +16,7 @@ stream {
         }
 
         server {
-            listen        {{ kube_apiserver_port }};
+            listen        127.0.0.1:{{ kube_apiserver_port }};
             proxy_pass    kube_apiserver;
             proxy_timeout 10m;
             proxy_connect_timeout 1s;