Use static::$kernel in runCommand() method (Test/WebTestCase.php)

When I run our test, it didn't release the resources (opened files, log, db connections) after the runCommand().
And there is no way to get the container for connection closing.
I modified the runCommand() method from the createClient() (Symfony\Bundle\FrameworkBundle\Test\WebTestCase).
Then I can get container by $container = static::$kernel->getContainer(), and close some resources.