Make kubelet_load_modules always present but false.

Update code and docs for that assumption.

roles/kubernetes/node/defaults/main.yml

@@ -33,3 +33,5 @@ etcd_config_dir: /etc/ssl/etcd
 # A port range to reserve for services with NodePort visibility.
 # Inclusive at both ends of the range.
 kube_apiserver_node_port_range: "30000-32767"
+
+kubelet_load_modules: false

roles/kubernetes/node/templates/kubelet-container.j2

@@ -14,7 +14,7 @@
   {% for dir in ssl_ca_dirs -%}
   -v {{ dir }}:{{ dir }}:ro \
   {% endfor -%}
-  {% if kubelet_load_modules is defined and kubelet_load_modules == true -%}
+  {% if kubelet_load_modules -%}
   -v /lib/modules:/lib/modules:ro \
   {% endif -%}
   -v /sys:/sys:ro \