Ensure alerts are generated if logging drops to 0

The ruby check uses "less than" or "greater than" operators not <= or
>=. Therefore a check looking for values below zero will never be
triggered by a value of zero. Zero is the lowest logging rate possible.
Merge pull request #681 from alphagov/fix-graphite-logging-rate-check

Ensure alerts are generated if logging drops to 0
Replace lumberjack with logstash-forwarder

 - Upgrading in the hope we will stop logstash running out of memory and
   crashing. If not at least we are running a later version of the
   software. This PR
   https://github.com/elasticsearch/logstash-forwarder/issues/212 seems
   to suggest there may be issues with logstash forwarder. These
   logstash Jira tickets are also relvant -
   https://logstash.jira.com/browse/LOGSTASH-1253
   https://logstash.jira.com/browse/LOGSTASH-2168
 - Switch to the official elasticsearch logstash forwarder repo. There
   were a couple of issues with this which we would like to fix
   upstream -
 - For now add a symlink to correct the location
   the init script looks for the config file, as this is wrong in either
   the logstash-forwarder deb package or the puppet module
   https://github.com/elasticsearch/puppet-logstashforwarder/pull/12
 - There is an issue with file ordering in the puppet module. This means
   sometimes deploying using this module will fail
   https://github.com/elasticsearch/puppet-logstashforwarder/pull/13
 - The changes to our actual puppet code were renaming config params,
   using a different class, and renaming the defines to match the new
   puppet modules.
Add in code to remove lumberjack

This is a hack involving using the lumberjack module init and logshipper
manifests as skeleton from which we hang a lot of ensure absents. This
will be removed in a further clean up pr.