Make sure global worker defs only done once

This commit makes sure that all the global definitions on the worker
class are only defined once. If we don't check for the previous
definition when running with multiple workers on a single node things
will fail.

Change-Id: I947d61f455778fe41d0a4723c99d029272d2155d

manifests/worker.pp

@@ -26,13 +26,17 @@ define subunit2sql::worker (
 ) {
   $suffix = "-${name}"
 
-  file { '/etc/logstash/':
-    ensure => absent,
+  if ! defined(File['/etc/logstash']) {
+    file { '/etc/logstash/':
+      ensure => absent,
+    }
   }
 
-  user { 'subunit':
-    ensure => present,
-    system => true,
+  if ! defined(User['subunit']) {
+    user { 'subunit':
+      ensure => present,
+      system => true,
+    }
   }
 
   if ! defined(File['/etc/subunit2sql']) {