private static void verifyAppPath(Curator zk, Path appPath) {
        if (!zk.exists(appPath))
            throw new RuntimeException("App with path " + appPath + " does not exist");
    }
Reads allocated hosts at the given node.

@return the allocated hosts at this node or empty if there is no data at this path
configserver/src/main/java/com/yahoo/vespa/config/server/zookeeper/ZKApplicationPackage.java