Fix adding disks to transient VMs

TestMachinesDisks.testAddDiskDirPool's "transient VM" test case
ommediately opened the "Add Disk" dialog after undefining the VM. This
was a race condition which the test actually "won" in most cases: The
`UNDEFINED` event did not yet bubble through the UI, so the "Add Disk"
dialog still thought that the VM was persistent. Fix that by waiting
until the UI picked up the event and considers the VM transient.

This exposed a bug in the dialog's fill() function: It tried to check
the value of the "Permanent" checkbox, but that doesn't exist at all for
transient VMs. Fix up the logic and assert the latter for transient VMs.

Now that this test is working correctly, it uncovered a bug in the code:
Trying to add a disk to a transient VM fails with

> Requested operation is not valid: transient domains do not have any persistent config

because the `persistent` state was initialized to "true". Fix that.

https://issues.redhat.com/browse/RHEL-17677

src/components/vm/disks/diskAdd.jsx

@@ -375,7 +375,7 @@ export const AddDiskModalBody = ({ disk, idPrefix, isMediaInsertion, vm, vms, su
         size: 1,
         unit: units.GiB.name,
         volumeName: "",
-        permanent: true,
+        permanent: vm.persistent,
     });
     const [mode, setMode] = useState(isMediaInsertion ? CUSTOM_PATH : CREATE_NEW);
     const [validate, setValidate] = useState(false);

test/check-machines-disks

@@ -640,8 +640,12 @@ class TestMachinesDisks(machineslib.VirtualMachinesCase):
                 b.select_from_dropdown(f"#vm-{self.vm_name}-disks-adddisk-existing-select-volume", self.volume_name)
 
             # Configure persistency - by default the check box is checked
-            if not self.permanent:
-                b.set_checked(f"#vm-{self.vm_name}-disks-adddisk-permanent", False)
+            if self.persistent_vm:
+                if not self.permanent:
+                    b.set_checked(f"#vm-{self.vm_name}-disks-adddisk-permanent", False)
+            else:
+                # checkbox not shown at all for transient VM
+                b.wait_not_present(f"#vm-{self.vm_name}-disks-adddisk-permanent")
 
             # Check non-persistent VM cannot have permanent disk attached
             if not self.persistent_vm:
@@ -1107,7 +1111,9 @@ class TestMachinesDisks(machineslib.VirtualMachinesCase):
             b.click("#vm-subVmTest1-system-run")
             b.wait_in_text("#vm-subVmTest1-system-state", "Running")
             # Test disk attachment to non-persistent VM
+            b.wait_visible(".vm-top-panel[data-vm-transient=false]")
             m.execute("virsh undefine subVmTest1")
+            b.wait_visible(".vm-top-panel[data-vm-transient=true]")
             self.VMAddDiskDialog(
                 self,
                 pool_name='myPoolOne',