Apply dom0 state as part of updater

[emkll]

Status

Ready for review

Description of Changes

Fixes #427

Applied dom0 salt state after applying VM upgrades. The reason it was done as part of the UpgradeThread thread is to ensure the user has consented to applying upgrades. It is also done after to ensure changes to dom0 config packages are applied.

Testing

• Ensure at least 1 VM needs updates (due to changes in apt server logic, it may be less easy to downgrade packages, I had to install a locally-built securedrop-client deb in sd-app-buster-template to ensure the apt server can update to the latest nightly version
• dom0 configuration is applied after upgrades are applied to VMs
• test coverage for Updater.py is 100%

Checklist

If you have made changes to the provisioning logic

• Linting (make flake8) and tests (make test) pass in dom0 of a Qubes install

[conorsch]

@emkll Merge of #450 introduced conflicts here, mind rebasing?

[emkll]

rebased on latest master

[conorsch]

Taking for a spin, will downgrade some packages prior to testing...

[conorsch]

Works as advertised. Confirmed dom0 update landed in logs, and monitored for qubesctl highstate process during the provisioning run.