Lowercase hosts on import and when adding to the whitelist

- Lowercase hosts when importing from site YAML files, so we don't potentially add uppercase hosts that Bouncer can't handle.
- Lowercase hosts when they're added to the whitelist.
Nothing is calling the implementation that this is testing, and if I delete it, the tests still pass. The reason for that is that this `it` block is inside a `before` block and so isn't being run. It would be nice if rspec complained but hey ho. This is one reason that writing failing tests before writing the implementation is a good idea.