@Override
        public String toString() {
            return "directory '" + name() + "'";
        }
Dumps the content of this and all children recursively to the given string builder.
Useful for debugging.

@param b the builder to write to
@param pathPrefix, the path to this node, never ending by "/"
zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java