@Override
    public void validateIncludeDir(String dirName) {
        Path path = Path.fromString(USERAPP_ZK_SUBPATH).append(dirName);
        if ( ! zkApplication.exists(path)) {
            throw new IllegalArgumentException("Cannot include directory '" + dirName +
                                               "', as it does not exist in ZooKeeper!");
        }
    }
Returns readers for all the children of a node.
The node is looked up relative to the location of the active application package in zookeeper.
configserver/src/main/java/com/yahoo/vespa/config/server/zookeeper/ZKApplicationPackage.java