private static Builder newBuilder(Class<? extends ConfigInstance> configClass) throws ReflectiveOperationException {
        Class<?> builderClazz = configClass.getClassLoader().loadClass(configClass.getName() + "$Builder");
        return (Builder)builderClazz.getDeclaredConstructor().newInstance();
    }
Populates an instance of configClass with config produced by configProducer.
config-model/src/main/java/com/yahoo/vespa/model/VespaModel.java