Add http_listener class to system.telegraf.agent

Change-Id: I5d24665c65d015942e563855cf2889a5431d85f2
diff --git a/telegraf/agent/init.yml b/telegraf/agent/init.yml
index 3f6133d..ca7e2b0 100644
--- a/telegraf/agent/init.yml
+++ b/telegraf/agent/init.yml
@@ -1,5 +1,6 @@
 classes:
 - service.telegraf.agent
+- system.telegraf.agent.input.http_listener
 - system.telegraf.sudo
 parameters:
   telegraf: