Drop DeviceInfo.data - device extension should provide a subclass with
proper individual fields.
Drop DeviceAssignment.frontend_domain - this information is redundant -
frontend domain is defined by where DeviceAssignment is attached.
Rename DeviceCollection.devclass to bus - devclass if confusing here,
because this term is also used for DeviceInfo subclass.
Setting VMProperty to None VM should be encoded as '' value (according
to VMProperty._none_value). But value validation rejected this value.
QubesOS/qubes-issues#2622
Accessing non-existing property is a common action (for example
hasattr() do try to access the property). So, introduce specific
exception, inheriting from AttributeError. It will behave very similar
to standard (non-Admin-API) property access.
This exception is reported to the Admin API user, so it will be possible
to distinguish between non-existing property and access denied. But it
isn't any significant information leak, as list of valid properties is
publicly available in the source code.
QubesOS/qubes-issues#853
