public TestRoot buildModel(String servicesXml) {
        return buildModel(servicesXml, "<hosts><host name='localhost'><alias>mockhost</alias></host></hosts>");
    }
Build a model from an XML string. The hosts referenced in services must be set to 'mockhost' when using
this method, as it automatically generates a hosts file for you.

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