Fixed creation of mock in tests for methods that are necessary.

Fixes tests:

```
PHPUnit 4.3.5 by Sebastian Bergmann.

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Time: 16.22 seconds, Memory: 62.50Mb

There was 1 error:

1) Sonata\AdminBundle\Tests\SonataAdminBundleTest::testBuild
PHPUnit_Framework_MockObject_RuntimeException: Cannot mock Symfony\Component\DependencyInjection\ContainerBuilder::addExpressionLanguageProvider() because a class or interface used in the signature is not loaded

/.../SonataAdminBundle/Tests/SonataAdminBundleTest.php:31

Caused by
ReflectionException: Class Symfony\Component\ExpressionLanguage\ExpressionFunctionProviderInterface does not exist

/.../SonataAdminBundle/Tests/SonataAdminBundleTest.php:31
```