VOL-1255: Fixed an issue with the proxy implementation

- Had to change the model slightly to mimic a polymorphic behaviour

Change-Id: I12017cdfedf5c0ed05243245aa2a811556222e0f
diff --git a/db/model/node_test.go b/db/model/node_test.go
index 29f4c7c..3b12c14 100644
--- a/db/model/node_test.go
+++ b/db/model/node_test.go
@@ -66,7 +66,7 @@
 		PmConfigs:       &voltha.PmConfigs{},
 		ImageDownloads:  []*voltha.ImageDownload{},
 	}
-	root := &Root{}
+	root := &root{}
 	txid := fmt.Sprintf("%x", md5.Sum([]byte("node_transaction_id")))
 
 	node := NewNode(root, data, true, txid)