Default firewall option

[soullivaneuh]

Lot of Symfony projet use only one main firewall, so we have to regularly to make this:

$this->loginAs($this->getReference('user_support'), 'main');

The main keyword is very redundant. It would be great to add a default_login_firewall parameter to the bundle in order to just do this:

$this->loginAs($this->getReference('user_support'));