qemu: Do not free the device from activePciHostdevs if it's in use

* src/qemu/qemu_hostdev.c (qemuDomainReAttachHostdevDevices):
pciDeviceListFree(pcidevs) in the end free()s the device even if
it's in use by other domain, which can cause a race.

How to reproduce:

<script>

virsh nodedev-dettach pci_0000_00_19_0
virsh start test
virsh attach-device test hostdev.xml
virsh start test2

for i in {1..5}; do
        echo "[ -- ${i}th time --]"
        virsh nodedev-reattach pci_0000_00_19_0
done

echo "clean up"
virsh destroy test
virsh nodedev-reattach pci_0000_00_19_0
</script>

Device pci_0000_00_19_0 dettached

Domain test started

Device attached successfully

error: Failed to start domain test2
error: Requested operation is not valid: PCI device 0000:00:19.0 is in use by domain test

[ -- 1th time --]
Device pci_0000_00_19_0 re-attached

[ -- 2th time --]
Device pci_0000_00_19_0 re-attached

[ -- 3th time --]
Device pci_0000_00_19_0 re-attached

[ -- 4th time --]
Device pci_0000_00_19_0 re-attached

[ -- 5th time --]
Device pci_0000_00_19_0 re-attached

clean up
Domain test destroyed

Device pci_0000_00_19_0 re-attached

The patch also fixes another problem, there won't be error like
"qemuDomainReAttachHostdevDevices: Not reattaching active
device 0000:00:19.0" in daemon log if some device is in active.
As pciResetDevice and pciReattachDevice won't be called for
the device anymore. This is sensible as we already reported
error when preparing the device if it's active. Blindly trying
to pciResetDevice & pciReattachDevice on the device and getting
an error is just redundant.

src/qemu/qemu_hostdev.c

@@ -414,8 +414,10 @@ void qemuDomainReAttachHostdevDevices(struct qemud_driver *driver,
          */
         activeDev = pciDeviceListFind(driver->activePciHostdevs, dev);
         if (activeDev &&
-            STRNEQ_NULLABLE(name, pciDeviceGetUsedBy(activeDev)))
+            STRNEQ_NULLABLE(name, pciDeviceGetUsedBy(activeDev))) {
+            pciDeviceListSteal(pcidevs, dev);
             continue;
+        }
 
         /* pciDeviceListFree() will take care of freeing the dev. */
         pciDeviceListSteal(driver->activePciHostdevs, dev);