kafkatee: webstats-collector, add ferm service

The webstats-collector opens the TCP port configured in $collector_port
which is currently 3815. There is no ferm service configured
for this yet though, so we can't apply base::firewall on the nodes
that are using this because it has a default DROP policy.

To be able to merge I5859dbce6da06a5e27, and then entirely get rid
of the old iptables class, we need to add ferm services for all (TCP)
services that are running on hosts that also have udp2log.

This is one of them, see the comments on the linked change for others.

Change-Id: Ibf3af60a8932325f12bf3bf97499459c454abba7
Merge "kafkatee: webstats-collector, add ferm service" into production