Just a suggestion:

We can add the omnibus block only when we have both `require_chef_omnibus` and `use_vagrant_provision` set.
```ruby
if config[:use_vagrant_provision]
  chef_block(arr)
  omnibus_block(arr) if config[:require_chef_omnibus]
end
```
This will make sure we don't add that config line when we don't want to use vagrant provision.