Utility method for getting unprivileged account name

[aral]

From lib/Util.js:

static unprivilegedAccountName () {
  if (process.platform === 'win32' || process.env.USER !== 'root') {
    // Does not apply to Windows as there is no sudo.
    return os.userInfo().username
  } else {
    return process.env.SUDO_USER
  }
}