vm: add vm.klass property
vm: add vm.klass property

Allow to get domain class as a property, not using admin.vm.List call.
This makes it unnecessary to call admin.vm.List on the client side to
construct wrapper object.

woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin