zabbix-agent: add 504 status to zabbix

roles/zabbix-agent/files/nginx-zabbix.pl

@@ -64,6 +64,7 @@ sub main {
 			404 => 0,
 			500 => 0,
 			502 => 0,
+			504 => 0,
 			other => 0,
 		},
 		# counter since prog start