vagrant up qemutest (downloads the qcow2 url and builds the box fine)
```
vagrant up qemutest
Bringing machine 'qemutest' up with 'libvirt' provider...
==> qemutest: Box 'debian10-20201010-1039' could not be found. Attempting to find and install...
qemutest: Box Provider: libvirt
qemutest: Box Version: >= 0
==> qemutest: Box file was not detected as metadata. Adding it directly...
==> qemutest: Adding box 'debian10-20201010-1039' (v0) for provider: libvirt
qemutest: Downloading: https://annex.softwareheritage.org/public/isos/libvirt/debian/swh-debian-10.6-amd64-20201010-1039.qcow2
qemutest: Progress: 32% (Rate: 8763k/s, Estimated time remaining: 0:00:41)
...
```