Improved test speed

Improved test speed (tests now run in 4m instead of 18m).

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | [yes]
| Fixed tickets | 
| BC Breaks     | 
| Doc           | 


## Depends

- https://github.com/symfony-cmf/Testing/pull/75
- https://github.com/sulu-cmf/SuluTestBundle/pull/25/files