Very few calls at client side really needs VM class name. So, even in
non-blind mode use just QubesVM class, to avoid strange cases depending
on blind mode being enabled or not. Then, have VM class name in 'klass'
property. If known at object creation time, cache it, otherwise query
qubesd at first access.
Since Admin API, qvm-ls takes a long time to complete. Therefore,
Corporate Headquarters commanded that a Enterprise Spinner is to be
implemented and mandated it's use unto us.
We take amusement from its endless gyrations.
Since migration to Admin API, qvm-ls no longer have list of all VM
properties in advance, so can't really validate fields list. Simply
assume that unknown columns are properties.
