qubes/app: create 'default' storage pool as LVM when present

When system is installed with LVM thin pool, it should be used by
default. But lets keep file-based on for /var/lib/qubes for some corner
cases, migration etc.

QubesOS/qubes-issues#2412

qubes/app.py

@@ -856,13 +856,16 @@ class Qubes(qubes.PropertyHolder):
             8: qubes.Label(8, '0x000000', 'black'),
         }
 
-        for name, config in qubes.config.defaults['pool_configs'].items():
-            self.pools[name] = self._get_pool(**config)
-
         # check if the default LVM Thin pool qubes_dom0/pool00 exists
         if os.path.exists('/dev/mapper/qubes_dom0-pool00-tpool'):
             self.add_pool(volume_group='qubes_dom0', thin_pool='pool00',
-                          name='lvm', driver='lvm_thin')
+                          name='default', driver='lvm_thin')
+        else:
+            self.pools['default'] = self._get_pool(
+                dir_path=qubes.config.qubes_base_dir,
+                name='default', driver='file')
+        for name, config in qubes.config.defaults['pool_configs'].items():
+            self.pools[name] = self._get_pool(**config)
 
         self.domains.add(
             qubes.vm.adminvm.AdminVM(self, None, qid=0, name='dom0'))

qubes/config.py

@@ -86,9 +86,10 @@ defaults = {
     'root_img_size': 10*1024*1024*1024,
 
     'pool_configs': {
-        'default': {'dir_path': qubes_base_dir,
+        # create file pool even when the default one is LVM
+        'varlibqubes': {'dir_path': qubes_base_dir,
                     'driver': 'file',
-                    'name': 'default'},
+                    'name': 'varlibqubes'},
         'linux-kernel': {
             'dir_path': os.path.join(qubes_base_dir,
                                      system_path['qubes_kernels_base_dir']),