async function isEmpty(selector) {
  const usersAtHome = await this.getUsersAtHome(selector);
  return usersAtHome.length === 0;
}
@public
@description Return true or false if house is empty.
@param {string} selector - Selector of the house.
@returns {Promise} Resolve with true if house is empty.
@example
const empty = await gladys.house.isEmpty('my-house');