fix meta/salt with missing pillar

Change-Id: Icfd2693b3622f40834831493ecd078e858d9d14e
diff --git a/telegraf/meta/salt.yml b/telegraf/meta/salt.yml
index 1e2330b..9a5ca1f 100644
--- a/telegraf/meta/salt.yml
+++ b/telegraf/meta/salt.yml
@@ -1,5 +1,5 @@
 grain:
-  {%- if pillar.telegraf.agent is defined %}
+  {%- if pillar.get('telegraf', {}).get('agent') %}
   {%- from "telegraf/map.jinja" import service_grains with context %}
   telegraf:
     {{ service_grains|yaml(False)|indent(4) }}