assert on savevm
Description of problem:

Steps to reproduce:
1. launch as above (n.b. qemu-img command: qemu-img create -f qcow2 rootfs.qcow2 60G
2. from qemu monitor: savevm test
3. On stderr

```
Assertion failed: (qemu_get_current_aio_context() == qemu_get_aio_context()), function bdrv_poll_co, file block-gen.h, line 43.
```
Additional information: