Add hide_create_volume to instance defaults

The commit [1] added the hide_create_volume option
this adds the default value for that.

[1] https://review.openstack.org/#/c/605813/

Change-Id: Ic0c79ed560348b570b57108e5cb7d7302ab0442c

manifests/init.pp

@@ -587,6 +587,7 @@ class horizon(
   $instance_defaults = {
     'config_drive'              => false,
     'create_volume'             => true,
+    'hide_create_volume'        => false,
     'disable_image'             => false,
     'disable_instance_snapshot' => false,
     'disable_volume'            => false,