Change .env to .env.production

:fork_and_knife: In service to https://github.com/opscode/supermarket/pull/399 this changes the .env template to be .env.production as we're now taking advantage of dotenvs environment features. .env.production will take precedence over .env.
We should use serverspecs builtin resource_types.

be_linked_to
In order to test a subject is linked to a given file or directory, you should use be_linked_to matcher.

```ruby
describe file('/srv/supermarket/current/.env.production) do
  it { should be_linked_to '/srv/supermarket/shared/.env.production' }
end
```