Add hidden attr to password in the Heat Templete

Now the pasword is exposed, but it should be a secret.
So we can add the "hidden" to protect it.
(http://docs.openstack.org/developer/heat/template_guide/hot_spec.html#parameters-section).

Change-Id: Idb291effb37ef0bf64e779a9e5fa7ee15162edaa

magnum/templates/kubernetes/kubecluster-fedora-ironic.yaml

@@ -103,6 +103,7 @@ parameters:
       fill in for Kubernetes config file
     default:
       ChangeMe
+    hidden: true
 
   tenant_name:
     type: string

magnum/templates/kubernetes/kubecluster.yaml

@@ -194,6 +194,7 @@ parameters:
       fill in for Kubernetes config file
     default:
       ChangeMe
+    hidden: true
 
   tenant_name:
     type: string