Add forward zones config

Change-Id: Ic42b37e1373d057b1559de321dd7ab9211defe06
diff --git a/defaults/main.yml b/defaults/main.yml
index 5ab724c..bf988ec 100644
--- a/defaults/main.yml
+++ b/defaults/main.yml
@@ -17,5 +17,8 @@
 # IP of authoritative nameserver that serves stub zones
 unbound_authoritative_server_ip: "127.0.0.1"
 
+# Forwarders
+unbound_forward_zones: []
+
 # DNS zones
 dns_zones: {}