Show pending notifications for a user.

def GetNotifications(user=None, token=None):
  """Show pending notifications for a user."""
  if not user:
    user = getpass.getuser()
  user_obj = aff4.FACTORY.Open(
      aff4.ROOT_URN.Add("users").Add(user), token=token)
  return list(user_obj.Get(user_obj.Schema.PENDING_NOTIFICATIONS))