CleanSave.__getattribute__ causes significant performance reduction

We have code in CleanSave.__getattribute__ which prevents attributes
that have been deferred to load. It makes sense, since we only defer
attributes if we don't want them to be loaded.

However, doing that check in CleanSave.__getattribute__ means that
it gets executed for every attribute access. That's very expensive.
Even if it takes a few microseconds to do the check, that can easily
add up to seconds in a request.

By moving that check to monkeypatch DeferredAttribute.__get__, the
websocket call to get the list of machines got almost twice as fast
as before.