Fix translations at login plugin
To be translatable text field should be marked
with @i18n. Also these messages should be provided by
i18n_messages.
Fixes: https://pagure.io/freeipa/issue/7559
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>