Generally things to be done with ``caddy-frontend``:
* implement back ``url`` and ``https-url`` on slave, that if ``https-url`` is defined it is used on HTTPS enabled part, and ``url`` is used on HTTP part
* tests: add assertion with results of promises in etc/promise for each partition
* check the whole frontend slave snippet with ``caddy -validate`` during buildout run, and reject if does not pass validation
* ``apache-ca-certificate`` shall be merged with ``apache-certificate``
