Add support for JSON request in HTTP test class
"urllib.parse.urlencode()" brokes JSON request's data.
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>