VirtualMachine: Refresh LVM cache before creating PV

When *lvmetad* is in use, it will cache volume group metadata from
previous runs of `mkvm` that used the same block device and prevent new
physical volumes from being created on it. Running `pvscan` alone does
not refresh the cache unless it is told to do so with the `--cache`
argument.

src/mkvm/storage.py

@@ -135,9 +135,12 @@ def partition_gpt(blockdev, partitions):
         raise DiskError('Failed to partition disk: {}'.format(msg))
 
 
-def pvscan():
+def pvscan(dev=None):
+    cmd = ['pvscan']
+    if dev:
+        cmd += ('--cache', dev)
     try:
-        output = subprocess.check_output(['pvscan'], stderr=subprocess.STDOUT)
+        output = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
         if output:
             log.debug('pvscan:\n{}'.format(output.decode().rstrip()))
     except subprocess.CalledProcessError as e:

src/mkvm/vmdesc.py

@@ -372,8 +372,7 @@ class VirtualMachine(object):
         storage.partition_gpt(self._disk.blockdev, self.partitions)
 
     def _partition_lvm(self):
-        blockdev = self._disk.blockdev
-        storage.pvscan()
+        storage.pvscan(self._disk.blockdev)
         pvs = []
         if self.partitions:
             partitions = self._disk.partitions
@@ -381,7 +380,7 @@ class VirtualMachine(object):
                 if part.get('type') == 0x8e00:
                     pvs.append(partitions[idx])
         else:
-            pvs.append(blockdev)
+            pvs.append(self._disk.blockdev)
         storage.create_lvm_pv(*pvs)
         storage.create_lvm_vg(self.vg_name, *pvs)
         for vol in self.volumes: