code: func (s *Docker) Run(cmd string, args ...string) (string, error) {
  	cmdArgs := make([]string, 0, len(args)+1)
  	cmdArgs = append(cmdArgs, cmd)
  	cmdArgs = append(cmdArgs, args...)
  
  	exe := exec.Command(s.binCmd, cmdArgs...)
  	var stdout, stderr bytes.Buffer
  	exe.Stdout, exe.Stderr = &stdout, &stderr
  
  	if err := exe.Run(); err != nil {
  		return stdout.String(), ExternalCmdError{
  			err, stderr.String(), stdout.String()}
  	}
  	return stdout.String(), nil
  }
docs: // Run executes especified command on Docker.
  //
  // Returns ExternalCmdError on error.