Fix forwarding options

[theofidry]

Currently we are using $input->getOptions(). It turns out it is not a good idea since when doing so it adds the default values of the options registered in the input definition. This is a problem as:

• Those added options may not be necessary (from a user perspective it's redundant)
• Those options includes "special options": options that are handled in a different way in Symfony*

*: Example of such a special option. When adding --version when calling your command, the Symfony application will directly handle it calling Application::getLongVersion() (in Application::doRun()) and not call the command at all.