clone(fromLabel, toLabel) {
    process.chdir(this.rootPath);
    let outputDir = quickTemp.makeOrReuse(this.dirs, toLabel);
    process.chdir(originalWorkingDirectory);

    this._conf.set(toLabel, outputDir);

    fs.copySync(this.get(fromLabel), outputDir);

    return this.dirs[toLabel];
  }
The `clone` method duplicates a cache. Some package managers can
leverage a pre-existing state to speed up their installation.

@method destroy
@param {String} fromLabel The label for the cache to clone.
@param {String} toLabel The label for the new cache.