Restore on clean system is convenient

[v6ak]

Long-term metatask.

Target scenario:

1. Install Qubes.
2. Install this backup system to dom0. (Even better: If this tool is integrated into Qubes, then this step would be unneeded.)
3. Create and install backup-storage VM for your backup backend. This might require installing some software to corresponding backup backend (e.g., Duplicity), but it should be as straightforward as possible.
4. (Maybe as a part of step 3.) Configure backup URL and credentials.
5. Run one simple command to restore it all. Minimum interaction is required from user at this moment. Or choose what to restore now and restore the rest later.

Results of the procedure:

• All VMs (AppVMs, TemplateVMs, HVMs, …) are restored.
• All VM config (firewall routes, VM drive size, …)
• User config of dom0 is restored. (Challenge, since we are restoring to a running system.)
• TODO: specify behavior for dom0 drivers etc. Maybe those should be optional, as one might want to perform restore on different hardware. Also, in some cases, drivers might be prerequisities of even starting the restore process.
• TODO: Specify behavior for volume layout. It might be useful to be preserved in some cases (e.g., laptop repaired), but this might be undesirable in other cases (e.g., completely new laptop).

TODO: list relevant issues.