Do not overwrite vagrant's cookbooks_path

In my chef repo, I'd like to have a single Berksfile and single virtual machine to test my cookbooks on. Nevertheless, vagrant-berkshelf overwrites default cookbooks_path for some reason. It wasn't like that until 685cabe2f8ab39335e756ffa9de4d069e73c3746.
The test I wrote is the most horrible test I made ever, so it might be better to not include it :)