Make the redirector build fail if any hosts are uppercase
Condense unique and lowercase checks into one

- This is so we don't iterate over all the hosts twice as this would
  cause the build to slow down.
Centralise `require`s in `lib/redirector`

* Make `test_helper` require that and any minitest dependencies
* To fix an environment-sensitive require order build failure
Rename the host validation rake task and methods to just be `validates`
Use the positive `uppercase.any?` instead of negative `.empty?`

- This makes it more readable.
- Also rename `uppercase` to `has_uppercase` - otherwise it sounds like
  a true/false value.
- Use `Set.new` instead of defining a hash for `has_uppercase` -
  slightly shorter and we weren't using the right hand side of the hash.
Merge pull request #1006 from alphagov/build_fails_if_uppercase_host

Make the redirector build fail if any hosts contain uppercase characters
Remove obsolete tld config

We now have IP addresses for our CDN which we use instead of having this
jury-rigged nginx config.
Fix typo