Add send_metadata_interval at 300s to debian

Previously, the send_metadata_interval for gmond was set at 0 for
Debian based systems, and 300 for Red Hat based systems.  This change
synchronizes the setting such that Debian is now 300s as well.

templates/gmond.conf.debian.erb

@@ -11,7 +11,7 @@ globals {
   host_dmax = 0 /*secs */ 
   cleanup_threshold = 300 /*secs */ 
   gexec = no             
-  send_metadata_interval = 0     
+  send_metadata_interval = 300 /*secs */
 } 
 
 /* If a cluster attribute is specified, then all gmond hosts are wrapped inside