Switch VM runtime

Use qemu instead of VirtualBox to execute the virtual machines. The advantage is a much faster and reliable startup of the VMs. With VirtualBox the image needs to be copied as well there were sometimes problems with the ssh connection to a running machine. With qemu the copy of the image isn't needed and no ssh problems were seen yet.

added CI/CD label

requested review from @p.-a.loizeau

assigned to @p.-a.loizeau

Dear @f.uhlig, @v.friese, @p.-a.loizeau,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged