backup: improve restoring HVMs from Qubes 3.2

Set kernel to '' - boot from VM's own bootloader.
Keep it on MiniOS-based stubdomain - otherwise Windows would not boot.

qubesadmin/backup/core2.py

@@ -289,7 +289,15 @@ class Core2Qubes(qubesadmin.backup.BackupApp):
             if value_is_default and value_is_default.lower() != \
                     "true":
                 vm.properties[attr] = value
-        vm.properties['virt_mode'] = 'hvm' if "HVm" in vm_class_name else 'pv'
+        if "HVm" in vm_class_name:
+            vm.properties['virt_mode'] = 'hvm'
+            vm.properties['kernel'] = ''
+            # Qubes 3.2 used MiniOS stubdomain (with qemu-traditional); keep
+            # it this way, otherwise some OSes (Windows) will crash because
+            # of substantial hardware change
+            vm.features['linux-stubdom'] = False
+        else:
+            vm.properties['virt_mode'] = 'pv'
         if vm_class_name in ('QubesNetVm', 'QubesProxyVm'):
             vm.properties['provides_network'] = True
         if vm_class_name == 'QubesNetVm':

qubesadmin/tests/backup/backupcompatibility.py

@@ -292,10 +292,12 @@ parsed_qubes_xml_r2 = {
         'test-testhvm': {
             'klass': 'StandaloneVM',
             'label': 'purple',
-            'properties': {'virt_mode': 'hvm', 'memory': '512'},
+            'properties': {'kernel': '', 'virt_mode': 'hvm', 'memory': '512'},
             'devices': {},
             'tags': set(),
-            'features': {'service.meminfo-writer': False},
+            'features': {
+                'service.meminfo-writer': False,
+                'linux-stubdom': False},
             'template': None,
             'backup_path': 'appvms/test-testhvm',
             'included_in_backup': True,
@@ -620,7 +622,10 @@ parsed_qubes_xml_v4 = {
         'test-hvm': {
             'klass': 'StandaloneVM',
             'label': 'purple',
-            'properties': {'virt_mode': 'hvm', 'maxmem': '4000'},
+            'properties': {
+                'kernel': None,
+                'virt_mode': 'hvm',
+                'maxmem': '4000'},
             'devices': {},
             'tags': set(),
             'features': {'service.meminfo-writer': False},

qubesadmin/tests/backup/v4-qubes.xml

@@ -262,6 +262,7 @@
         <property name="maxmem">4000</property>
         <property name="name">test-hvm</property>
         <property name="qid">9</property>
+        <property name="kernel"></property>
         <property name="uuid">9909066b-0f03-4725-ad9e-fa3561d5566e</property>
       </properties>
       <features>