feat(instances): a VM's clone form in device cards, with fixes to what it clones

Settings > Clone was a horizontal form with unlabelled checkboxes. The
owner chose this layout from three rendered options: the clone's name
on top, a "Network" card with a new MAC address per NIC, a "Storage"
card with a new volume name per disk, then the optional title and
description and a footer with Clone.

Codex reviewed cloning end to end; these are fixed:

- Every NIC of the clone gets a new random MAC when the form opens.
  Only the first did, so a VM with two NICs gave its clone the second
  NIC's MAC. Guess MAC is offered for the first NIC only: a name's DHCP
  host entry holds one address.
- A VM without a NIC can be cloned: the first NIC's MAC was required.
- The disk name script uses the persistent disks, as the form does; a
  disk added pending the next start kept the source's volume name.
- A running or paused VM is not cloned while a copied disk changes at
  the next start: the backup copies the running disk, so the clone
  would get the old contents under the new definition.
- A derived volume name that does not start with the source's name now
  starts with the clone's name and the disk's device, so a second clone
  or a second disk does not take the same name.
- Guess for the clone name says when the DHCP file has no free name; it
  stopped with a script error.
- The qcow2 metadata preallocation box shows only for a shut-off VM: a
  live clone's backup ignores it.

Other users no longer get hidden MAC and disk inputs or the scripts that
filled them: the server derives those values and ignored the posted ones.

vrtManager/instance.py

@@ -2467,6 +2467,11 @@ class wvmInstance(wvmConnect):
                 raise util.OperationError(f"Disk {dev} is not a local file; shut the VM down to clone it")
             if source.getparent().find("shareable") is not None:
                 raise util.OperationError(f"Disk {dev} is shareable; shut the VM down to clone it")
+        # the backup copies the running disks: one the next start changes would give the clone the wrong data
+        live = etree.fromstring(self._XMLDesc(0))
+        for source, dev in disks:
+            if live.xpath("devices/disk[target/@dev=$dev]/source/@file", dev=dev) != [source.get("file")]:
+                raise util.OperationError(f"Disk {dev} changes at the next start; shut the VM down to clone it")
         if self.instance.jobInfo()[0] != VIR_DOMAIN_JOB_NONE:
             raise util.OperationError("Another job is running on the VM; clone it when that ends")