Comment 2 for bug 1641210

I'm not sure if it's accessible from the validations but they are in the mistral environment for the plan (e.g. `mistral environment-get overcloud` for the default plan) in the parameter_defaults. They might not exist in the environment though if the user didn't override them. I'm not sure if there's a way to get to them besides hardcoding the default, lLooks like the defaults come from THT at the moment: https://github.com/openstack/tripleo-heat-templates/blob/master/puppet/services/neutron-plugin-ml2.yaml#L26 and #L60 too.