Hmm, I meant we can test 'qcow2' and 'raw' at the same time with variants like this:
```
variants:
          - qcow2:
          - raw:
variants:
...
```
Because there is no relative with vms, the only 'qcow2' in configuration will be useless.
And we won't disturb configuration during testing if possible. BTW, don't forget 'vms='', main_vm='',start_vm = no'