Fix for incorrect naming of all plugin migrations

As default after the Oct 17 changes, the schema.php files will all have a class name of AppSchema instead of the plugin name.

The current only solution is to run your command as Console/cake Migrations.migration generate --plugin MyPlugin --schema-class  MyPlugin

This was not an issue in v 2.3.2, so this became an issue in 2.3.3 or above.