tests: allow audiovm access is_preload property

Similar to QubesOS/qubes-mgmt-salt-dom0-virtual-machines#86

Author: marmarek

qubes/tests/integ/audio.py

@@ -122,6 +122,7 @@ def create_audio_vm(self, backend, start=True):
 admin.vm.property.Get               +xid     {vm}     @tag:audiovm-{vm}  allow   target=dom0
 admin.vm.property.Get               +stubdom_xid     {vm}     @tag:audiovm-{vm}  allow   target=dom0
 admin.vm.property.Get               +virt_mode     {vm}     @tag:audiovm-{vm}  allow   target=dom0
+admin.vm.property.Get               +is_preload     {vm}     @tag:audiovm-{vm}  allow   target=dom0
 admin.vm.feature.CheckWithTemplate  +audio   {vm}     @tag:audiovm-{vm}  allow   target=dom0
 admin.vm.feature.CheckWithTemplate  +audio-model   {vm}     @tag:audiovm-{vm}  allow   target=dom0
 """.format(