private static void validateRouting(Execution execution) {
        new RoutingValidator().validate(execution);
    }
Validates the model supplied, and if there already exists a model for the application validates changes
between the previous and current model

@return a list of required changes needed to make this configuration live
@throws ValidationOverrides.ValidationException if the change fails validation
config-model/src/main/java/com/yahoo/vespa/model/application/validation/Validation.java