Configurator: require DIC only once

When I use Configurator in tests to build DIC to run integration test. When used in combination with Nette/Tester and data providers, the setup method builds the container repeatedly, and not even hacking the container doesn't work

```php
$config->addParameters(array('container' => array('class' => 'SystemContainer_'  . md5(microtime()) )))
```

because there are other generated classes (generated interface factories) which have the exactly same class.