vm.get_power_state() have specifically documented 'NA' state for cases
when it's unable to get VM's power state. Use this when qrexec policy
forbid checking it.
Reported by @pietrushnic
FixesQubesOS/qubes-issues#3179
First, TemplateVM is not used anymore (see previous commit). Second,
don't harcode on client side that "only TemplateVM can be a template for
any VM" (which actually isn't true: AppVM can be a template for DispVM).
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.
This is a wrapper to use `$dispvm` target of qrexec call, just like any
other service call in qubesadmin module - using vm.run_service().
When running in dom0, qrexec-client-vm is not available, so DispVM needs
to be created "manually", using appropriate Admin API call
(admin.vm.CreateDisposable).
QubesOS/qubes-issues#2974
Since we use qubes.VMShell service now and send requested command on its
stdin, we need to terminate that shell after requested command -
otherwise the service will not terminate automatically waiting for
further input (next commands).
