private static String getIdString(Element spec) {
        String idString = XmlHelper.getIdString(spec);
        if (idString == null || idString.isEmpty()) {
            idString = spec.getTagName();
        }
        return idString;
    }
Creates all the config models specified in the given XML element and
passes their respective XML node as parameter.

@param root The Root to set as parent for all plugins
@param servicesRoot XML root node of the services file
config-model/src/main/java/com/yahoo/config/model/ConfigModelRepo.java