os.path.splitext fails on path without proper file base name, like
'/something/..000'. Use plain string methods (rsplit).
FixesQubesOS/qubes-issues#3167
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.
Abort tar process after extracting requested files - do not parse the
archive until the end (possibly tens of GB later).
FixesQubesOS/qubes-issues#2986
