Check that the latest telegraf package is installed

This patch fixed the next issue: during telegraf
upgrade from old versions salt formula doesn't upgrade
telegraf package if the newest version is available

PROD-35646

Change-Id: Ia9353ab06e05bfb715cad04e6ab4f1079959d978
diff --git a/telegraf/agent.sls b/telegraf/agent.sls
index 76d23b1..c0b5b53 100644
--- a/telegraf/agent.sls
+++ b/telegraf/agent.sls
@@ -3,7 +3,7 @@
 {%- if agent.get('enabled', False) %}
 
 telegraf_packages_agent:
-  pkg.installed:
+  pkg.latest:
     - names: {{ agent.pkgs }}
 
 telegraf_config_agent: