Guest os=Windows , qemu. Shutdown very slow. Memory allocation issue.
Description of problem:
simplifiying - libvirt config:
```
<memory unit='KiB'>33554432</memory>
  <currentMemory unit='KiB'>131072</currentMemory>
```
when use `<currentMemory>` less than `<memory>` - at/after shutdown of guest os cpu hangs on 100% and lasts long- approximately 3-5 minutes
if change to
```
<memory unit='KiB'>33554432</memory>
  <currentMemory unit='KiB'>33554432</currentMemory>
```
then shutdown takes less some seconds

problem occurs not (shutdown of VM takes some seconds) in cases when not used balloon device:
1 `<currentMemory>` equal to `<memory>`
2 memballoon driver disabled in windows
3 memballoon disabled on libvirt with "model=none" (and therefore not passed to qemu command line)
Additional information:
on the guest :
 * used drivers from virtio-win-0.1.262.iso - membaloon ver 100.95.104.26200 
 * possible combination of all or some components 

monitored next: 
`virsh dommemstat VMName` at shutdown time there grows "rss" till MaxMem, but very slowly.
aLso on `virsh setmem VMName --live --size 32G` 
rss grows slow - but takes 2 times less than at simple shutdown time ( = at shutdown seems occurs memory allocation and deallocation at the same time)

so something with some or all libvirt/qemu/balloon parts not so nice