PT-1914 Column data lost when 'Generated' is in the column comment (#482)

* PMM-1914 Fixed column parsing having generated

Fixed table parser code that errouneously considered a column as
generated when the default was empty DEFAULT '' and the COMMENT had
the word 'Generated'.

* PMM-1914 Updated TableParser in all programs

* PT-1914 Updated changelog

* PT-1914 Added test

t/pt-online-schema-change/samples/pt-1914.sql

@@ -0,0 +1,18 @@
+DROP DATABASE IF EXISTS test;
+CREATE DATABASE test;
+USE test;
+
+CREATE TABLE `aaa` (
+ `id` int(11) NOT NULL AUTO_INCREMENT,
+ `Password` varchar(100) NOT NULL DEFAULT '' COMMENT 'Generated',
+ `v` int(11) DEFAULT NULL,
+ PRIMARY KEY (`id`)
+) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;
+
+INSERT INTO test.aaa VALUES 
+(1, "a", 1), 
+(2, "b", 2), 
+(3, "c", NULL),
+(4, "d", 4),
+(5, "e", NULL), 
+(6, "f", 6);