Change paths to also cover legacy

The generic login was made to use `/login` and `/logout` URLs but the legacy (admin2) uses `/user/<action>`

Since the [BrowserContext#L74](https://github.com/ezsystems/BehatBundle/blob/master/Context/BrowserContext.php#L74) has basic/default URLs defined, and we can also defined the legacy ones, changed the generic authentication to work also on admin2 interface