Add logstash config for udp2log

Add logstash configuration file to process log events forwarded from
a udp2log daemon. This is not the prettiest way to receive log events as
the udp2log protocol is heavily biased towards producing line oriented
output suitable for appending to a flat file. It is however a quick and
dirty way to get a log event stream from an existing wiki farm flowing
into a logstash instance.

Change-Id: I70e4c20661f57b16ac5791af88a37fe254b4a68f