Varnish recipe breaks when using Chef Solo

```
NoMethodError: undefined method `each' for nil:NilClass
/tmp/heat_chef/79f870fb-8a57-46d9-ae98-14f84ff9b1ca/cookbooks/phpstack/recipes/varnish.rb:51:in `from_file'
```

https://github.com/rackspace-cookbooks/phpstack/blob/43f294b965d2b8636895847072c7226a2305b63c/recipes/varnish.rb#L51

`backend_nodes` is set to `nil` and you can't iterate over nada. :ghost: