Add support for Accept-Language in HTTP test class
"Accept-Language" is used to test translations.
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>