PT-181 online-schema-change not in sync with modules

- Modules updated
- Improved tests

t/pt-online-schema-change/samples/slave_lag.sql

@@ -37,7 +37,7 @@ DROP TABLE IF EXISTS `pt178`;
 /*!40101 SET character_set_client = utf8 */;
 CREATE TABLE `pt178` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
-  f1 VARCHAR(30) NULL,
+  f1 VARCHAR(30) DEFAULT '',
   f2 BIGINT(11) DEFAULT 0,
   PRIMARY KEY(id)
 ) ENGINE=InnoDB;