private void writeDir(ApplicationFile file, Path zooKeeperAppPath) throws IOException {
            writeDir(file, zooKeeperAppPath, (__) -> true);
        }
Writes some application package files into ZK - see write(app).

@param app the application package to use as input.
@throws IOException if not able to write to Zookeeper
configserver/src/main/java/com/yahoo/vespa/config/server/deploy/ZooKeeperDeployer.java