e511b70d8f
bd9c664b1a tried to remove it and use
the system resolver. However, we found that debian has a quirk that it adds
it adds the fqdn as 127.0.1.1. This means that the docker containers
resolve the my.example.com domain to that and can't connect.
This affects any apps doing a turn test (CLOUDRON_TURN/STUN_SERVER)
and also apps like SOGo which use the mail server hostname directly (since
they require proper certs).
https://www.debian.org/doc/manuals/debian-reference/ch05.en.html#_the_hostname_resolution
So, the solution is to go back to unbound, now that port 53 binding is specially
handled anyway in docker.js