Give more info about foreign keys

This helps when the table itself doesn't have foreign keys defined but if there are other tables with foreign keys pointing to the table on which gh-ost runs.

This gives INFO messages for each FK. Note that it now informs the user about `payment` being involved.
```
$ ./gh-ost -database sakila -table rental -alter 'ADD COLUMN ghost_test_001 tinyint DEFAULT NULL' -port 19590 -user msandbox -password msandbox -verbose
2016-08-03 10:18:45 INFO starting gh-ost 1.0.8
2016-08-03 10:18:45 INFO Migrating `sakila`.`rental`
2016-08-03 10:18:45 INFO connection validated on 127.0.0.1:19590
2016-08-03 10:18:45 INFO User has ALL privileges
2016-08-03 10:18:45 INFO binary logs validated on 127.0.0.1:19590
2016-08-03 10:18:45 INFO Restarting replication on 127.0.0.1:19590 to make sure binlog settings apply to replication thread
2016-08-03 10:18:46 INFO Table found. Engine=InnoDB
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`payment` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 INFO Found foreign key on `sakila`.`rental` related to `sakila`.`rental`
2016-08-03 10:18:47 ERROR Found 4 foreign keys related to `sakila`.`rental`. Foreign keys are not supported. Bailing out
2016-08-03 10:18:47 FATAL 2016-08-03 10:18:47 ERROR Found 4 foreign keys related to `sakila`.`rental`. Foreign keys are not supported. Bailing out
```

Related Issue: #129

Author: dveeden

go/logic/inspect.go

@@ -312,7 +312,7 @@ func (this *Inspector) validateTable() error {
 // validateTableForeignKeys makes sure no foreign keys exist on the migrated table
 func (this *Inspector) validateTableForeignKeys() error {
 	query := `
-		SELECT COUNT(*) AS num_foreign_keys
+		SELECT TABLE_SCHEMA, TABLE_NAME
 		FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
 		WHERE
 				REFERENCED_TABLE_NAME IS NOT NULL
@@ -322,8 +322,10 @@ func (this *Inspector) validateTableForeignKeys() error {
 	`
 	numForeignKeys := 0
 	err := sqlutils.QueryRowsMap(this.db, query, func(rowMap sqlutils.RowMap) error {
-		numForeignKeys = rowMap.GetInt("num_foreign_keys")
-
+		fkSchema := rowMap.GetString("TABLE_SCHEMA")
+		fkTable := rowMap.GetString("TABLE_NAME")
+		log.Infof("Found foreign key on %s.%s related to %s.%s", sql.EscapeName(fkSchema), sql.EscapeName(fkTable), sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
+		numForeignKeys++
 		return nil
 	},
 		this.migrationContext.DatabaseName,
@@ -335,7 +337,7 @@ func (this *Inspector) validateTableForeignKeys() error {
 		return err
 	}
 	if numForeignKeys > 0 {
-		return log.Errorf("Found %d foreign keys on %s.%s. Foreign keys are not supported. Bailing out", numForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
+		return log.Errorf("Found %d foreign keys related to %s.%s. Foreign keys are not supported. Bailing out", numForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
 	}
 	log.Debugf("Validated no foreign keys exist on table")
 	return nil