vagrant-berkshelf plugin always runs when directory contains a Berksfile

[ezekg]

Even if the Vagrantfile does not use vagrant-berkshelf, it still runs. We're using Berkshelf to vendor cookbooks, and shipping with the vendored cookbooks so that the end-user does not need ChefDK or Berkshelf installed. If the user happens to have this plugin installed but not ChefDK, the provisioning will fail. I don't really understand why this plugin is auto-enabling itself.