Use fedora-32 for sys-* VMs

[conorsch]

Towards/related to #640

It's that time again: Fedora 31 hits EOL on 2020-11-24: https://www.qubes-os.org/news/2020/10/27/fedora-31-approaching-eol/ which gives us about a month to migrate installs over to F32.

Let's aim to do it after the upcoming 0.5.0 release (#624).

[conorsch]

Starting on this today. In order to upgrade from F31 -> F32, normally all we have to do is update a single variable (and corresponding references in the tests), cf. #555. Due to the salt/updater failure in QubesOS/qubes-issues#6188, however, an error is encountered with that naive approach:

Configure Fedora-based system VMs
[ERROR   ] Command 'sudo qubesctl --skip-dom0 --targets fedora-32 state.sls update.qubes-vm' failed with return code: 20
[ERROR   ] stdout: fedora-32: ERROR (exit code 20, details in /var/log/qubes/mgmt-fedora-32.log)
[ERROR   ] retcode: 20
[ERROR   ] {'pid': 19032, 'retcode': 20, 'stderr': '', 'stdout': 'fedora-32: ERROR (exit code 20, details in /var/log/qubes/mgmt-fedora-32.log)'}

We can try adding a sed command to the f32 bootstrapping tasks to handle the dnf packaging pinning. Will test that today.