logstash: Add support for fatalmonitor dashboard

Add a "fatalmonitor" tag to events roughly equivalent to the script that
can be run on fenari.wikimedia.org. In addition to tagging it also adds
a "normalized_message" field that strips common noise words from the
message to make counting duplicate events easier.

Change-Id: I90c890c2a63b7b3c2ce98ac8d4c53709d12addae
Merge "logstash: Add support for fatalmonitor dashboard" into production