node: system container mounts /rootfs rslave

Already done for the Docker container:
openshift/openshift-ansible#3727

Signed-off-by: Giuseppe Scrivano <[email protected]>

Author: giuseppe

images/node/system-container/config.json.template

@@ -270,7 +270,7 @@
 	    "destination": "/rootfs",
 	    "options": [
 		"rbind",
-                "rprivate",
+                "rslave",
 		"ro"
 	    ]
         },