Berksfile support for temporary directory sync

Hi,

There was an bug in berksfile support in case you used a directory outside of kitchen. In that case it would not work. Please merge this fix to get it working. 
This change is breaking the build. Why did you change the variable name? You are only setting the new variable in config in case env.berksfile is not None, which breaks everything else.

I think what you wanted to do is this: `cookbook_paths += env.cookbook_search_paths`
instead of the opposite