execDirRecursive(path, options) {
    const self = this;
    const results = [];
    walkDirRecursive(path, pth => {
      const result = self.execDir(pth, options);
      results.push(result);
    });

    return results;
  }
Recursively executes `execDir`.
For use with `ls -R`.

@param {String} path
@param {Object} options
@return {Array} results
@api private