Deploy environment files were loaded after config/deploy.rb was loaded,
meaning if we used settings like `deploy_to` or `current_path` to set
variables inside the config/deploy.rb file, we'd be using the default
settings instead of the ones dictated by the deploy environment files.
These files are only loaded when the stage already has the value set
inside them, so we don't need to set it again.
On the other hand, the `rails_env` setting is configured in the
`config/deploy.rb` file.
