Create a second logstash instance and wire up
Reconfigure logstash_is_down alert
Remove ensure absent as file will have gone
Call logstash agents agent-1 and agent-2

This includes blasting the /etc/logstash directory to clean out the old
'agent' agent.
Configure lumberjack for both logstash agents

There are now 2 logstash agents. The bumped version of puppet-lumberjack
switches the host and port params for a single hosts param which takes
an array of strings in the form '<host>:<port>'.
Merge pull request #158 from alphagov/multiple-logstash

Multiple logstash