AppManager: Always default to default cluster.

Change-Id: I36ca1d710092cb3214d77ef24434ca817ba0b64d
diff --git a/core/installer/derived.go b/core/installer/derived.go
index 6c1305c..ada4e95 100644
--- a/core/installer/derived.go
+++ b/core/installer/derived.go
@@ -218,6 +218,9 @@
 		v, ok := derived[k]
 		// TODO(gio): if missing use default value
 		if !ok {
+			if def.Kind() == KindCluster {
+				ret[k] = "default"
+			}
 			continue
 		}
 		switch def.Kind() {