Not sure if this is the best place for this logic, but not sure how else to get `@provisioning_path` to be available like so [in *plugins/provisioners/chef/config/chef_solo.rb*](https://github.com/mitchellh/vagrant/pull/1897/files#L1R60):

```rb
@file_cache_path = @provisioning_path if \
  @file_cache_path == UNSET_VALUE
```

Would the solution be to move @provisioning_path definition into both *plugins/provisioners/chef/config/chef_solo.rb* and *chef_client.rb*, rather than *base.rb*