Remove redundant log fields.

* modules/openstack_project/templates/logstash/agent.conf.erb: Remove
logdate and logmessage fields when we are done with them. This reduces
the size of each log event.

Change-Id: I0b102d437397858d07cfc38498bc6b431199d3a4
Reviewed-on: https://review.openstack.org/26531
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins

agent.conf.erb

@@ -41,6 +41,11 @@ filter {
     exclude_tags => "_grokparsefailure"
     replace => [ "@message", "%{logmessage}" ]
   }
+  mutate {
+    type => "jenkins_console"
+    exclude_tags => "_grokparsefailure"
+    remove => [ "logdate", "logmessage" ]
+  }
 }
 
 <%= scope.function_template(['openstack_project/logstash/redis-output.conf.erb']) %>