Implement suspend and resume of VM

### Description

Seems like QMP has these nice commands:

**stop**
Suspend execution of VM

**cont**
Reverse a previous stop command - resume execution of VM.

https://en.wikibooks.org/wiki/QEMU/Monitor#Virtual_machine

Allows you to suspend and resume the VM, through qmp.sock:

```
Welcome to the QMP low-level shell!
Connected to QEMU 4.2.1
(QEMU) stop
{"return": {}}
(QEMU) cont
{"return": {}}
```