[COOK-2987] Mysql windows fixes

https://tickets.opscode.com/browse/COOK-2987

Improved the mysql cookbook on the Windows platform.

* copy the default database created by the installer to data_dir
* support custom installation directory
* use execute instead of windows_batch due to return code handling
* allow better customisation of my.cnf (similar to unix)
* more robust handling of test database deletion by adding IF EXISTS to the delete statement