Use getInternalRequest to return Symfony\Component\BrowserKit\Request

Symfony 2.3 getRequest returns Symfony\Component\HttpFoundation\Response,
which does not have a getCookies method. Use getInternalRequest to return
Symfony\Component\BrowserKit\Request, which does.
Merge pull request #814 from UseAllFive/fix-get-cookies-error

Use getInternalRequest to return Symfony\Component\BrowserKit\Request