Includes tests and simplified unmarshal test.

There's no point doing so much manual work and testing just to keep fields under a "attrs" key when marshalling to JSON. When creating the object we can just: 1. Marshal the object to JSON 2. Put it all under a "attrs" key. Now it's easier to imagine the mapping of the structs to JSON, since they follow the same rules as everything else in Go.

While here also don't log messages in testing unless there's an error.

I was excluding some struct fields so I thought I'd need to do some custom marshalling . But you don't need to do this as you can use struct tags to optionally exclude things from being put into JSON. Now there's no longer duplicate code between struct tags and keys in a map when marshalling. Handy!

We were missing some attributes, like not adding any groups or display names. This also adds a test which checks whether we are marshalling hosts into JSON correctly.