Clear node list to avoid memory leak, fixes #402

dbutils.c

@@ -2628,6 +2628,8 @@ witness_copy_node_records(PGconn *primary_conn, PGconn *witness_conn)
 	/* and done */
 	commit_transaction(witness_conn);
 
+	clear_node_info_list(&nodes);
+	
 	return true;
 }