WIP: Berksfile support

Reworked Berksfile support. There is one more thing to solve to properly use Berkshelfe we should not use any local cookbooks and only use cookbooks from Berksfile. Otherwise I use temporary directory for berks vendor if it's not said other way.

1) README
2) tests 

Will be done after initial approval.
This can also be put inside the outer else. If there is no config section it will never be executed anyway.