Add mqtt output plugin to logstash indexers

This commit adds support for configuring the mqtt logstash output
plugin. This will enable us to push events from our logstash workers
to firehose.o.o. The plugin can be found here:

https://github.com/kompa3/logstash-output-mqtt (althought it's README
is from a template and you have to look at the inline docs for how
to use it)

and the gem is published on rubygems.org here:

https://rubygems.org/gems/logstash-output-mqtt/

Change-Id: I7255f6c256ab3e3ca33caf69b71bf4ffab02c1bb

manifests/indexer.pp

@@ -31,6 +31,8 @@ class logstash::indexer (
   $conf_template   = undef,
   $input_template  = 'logstash/input.conf.erb',
   $output_template = 'logstash/output.conf.erb',
+  $enable_mqtt = false,
+  $mqtt_ca_cert_contents = undef,
 ) {
   include ::logstash
 
@@ -84,7 +86,22 @@ class logstash::indexer (
     mode    => '0644',
     require => Class['logstash'],
   }
+  if $enable_mqtt {
+    exec {'install_mqtt_plugin':
+      command => '/opt/logstash/bin/plugin install logstash-output-mqtt',
+      before  => Service['logstash'],
+      onlyif  => '/opt/logstash/bin/plugin list logstash-output-mqtt',
+    }
 
+    file { '/etc/logstash/mqtt-root-CA.pem.crt':
+      ensure  => present,
+      content => $mqtt_ca_cert_contents,
+      owner   => 'logstash',
+      group   => 'logstash',
+      mode    => '0600',
+      notify  => Service['logstash']
+    }
+  }
   service { 'logstash':
     ensure    => running,
     enable    => true,