The current production docker verison or configuration only allows to
forward a port either by using udp or tcp, not both (even though that's
what is suggested by fluentd).
docker will use the last entry and silently delete the former.

This is not a problem for us since we only talk to fluentd via tcp.

(for consistency, it's not strictly necessary)

This would only be a problem if fluentd wasn't running, but
since fluentd doesn't log to fluentd, kibana wouldn't help anyway.

It didn't include pdas before

Resolve "Integrate ELK stack with Fluentd"

Closes #9

See merge request !17

It's still very similar to dev, common configs could be extracted

Use IMAGE:latest as cache-from source for non-master builds

See merge request !16

Non-master builds are not pushed, so we can only use the master builds
as cache.