Migrate to official logstash packages; build out test framework; HAproxy; Nginx; UUID

This PR is designed to (at least partially) un-diverge a bunch of branches:

* pkg_update
* statsd_and_archive_replay
* x_request_id

It does the following:

* Migrates to the use of the elasticsearch logstash repo
* Upgrades to logstash v1.4.2
* Moves to 'conf.d' format configuration
* Adds a 'per-filter file' configuration testing framework in custom-test/
* Adds prefixes to any use of 'kv' -- we were overwriting fields like 'type'.

I have not focussed on maintaining compatibility with the various branches -- the field names will in many places will be different. We were doing things quite badly though, so this should be considered a base to move forwards from.

I've tried to make an effort to conform to a 'best practices guide' that I'm putting together, an early version is available at: https://gist.github.com/mikepea/443d1e07c430d447fd73 


You have spotted my deliberate mistake. I put type=audit across without tests, cos it didn't have any to begin with. Turns out it's super broken, so I'm writing some tests now.