public TestRoot buildModel(String servicesXml, String hostsXml) {
        if (!servicesXml.contains("<services")) {
            servicesXml = "<services version='1.0'>" + servicesXml + "</services>";
        }
        return buildModel(new MockApplicationPackage.Builder().withHosts(hostsXml).withServices(servicesXml).build());
    }
Build a model from an XML string of services and one of hosts.

@param servicesXml The xml for services.xml
@param hostsXml The xml for hosts.xml
@return a producer root capable of answering getConfig requests.
config-model/src/main/java/com/yahoo/config/model/test/TestDriver.java