code: func getDriveLetterByDiskNumber(diskNum string, exec Exec) (string, error) {
  	cmd := fmt.Sprintf("(Get-Partition -DiskNumber %s).DriveLetter", diskNum)
  	output, err := exec.Run("powershell", "/c", cmd)
  	if err != nil {
  		return "", fmt.Errorf("azureMount: Get Drive Letter failed: %v, output: %q", err, string(output))
  	}
  	if len(string(output)) < 1 {
  		return "", fmt.Errorf("azureMount: Get Drive Letter failed, output is empty")
  	}
  	return string(output)[:1], nil
  }
docs: // Get drive letter according to windows disk number