[2.1] Use routes for security paths

[wouterj]

Since Symfony2.1, it is recommend to use routenames for security paths. It is already fixed for the form_login options (see #2146 ) but we should also do this for the failure_path and default_target_path. I have found the use of these settings in cookbook/security/form_login, but there can be other articles aswell.

Todo

• Test if these options will work with routes

[weaverryan]

FYI default_target_path definitely works (see #2146) and so I imagine the other does as well.