Always-valid password in config

[vibby]

Thank you for the effort !

I am requesting one feature here : I use Behat on my php project to make end-to-end tests. I cannot test forms with captcha fields since I cannot predict the result.
Could it be possible to have a config parameter that would be an answer to the captcha challenge always saying yes. The option could be deactivated as a default for security reason.
I will try to propose a PR if your are ok with that idea.