minor fixes in the Bundle configuration

 Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | [![Build Status](https://travis-ci.org/symfony-cmf/BlockBundle.png?branch=config_tweaks)](https://travis-ci.org/symfony-cmf/BlockBundle)
| Fixed tickets | -
| License       | MIT
| Doc PR        | -