QEMU crashes after host time moves backwards
Description of problem:
QEMU process crashes after time synchronized and moved backwards on the host.
Steps to reproduce:
As detailed in the [thread](https://bugzilla.redhat.com/show_bug.cgi?id=2228406)

1. create a virtual machine and change tick period in the guest
2. executing `while [ 1 ];do hwclock --systohc; hwclock --hctosys;done` on the host