Factory reset and scheduled restore

[DigitalBrains1]

If you restore a backup with restore.py but don't finish the process (perhaps because you bricked your Precursor per #610), and then do precursorupdater --factory-reset, your Precursor will keep prompting for a backup key to finish the restoration process.

As bunnie found out at 38C3, this was due to a flag in flash not being erased by precursorupdater --factory-reset. The flag indicates that we are currently doing a restoration, but we actually cleared (part of) the PDDB and there is no restoration image to process. Clearing the flag allows us to reinitialize the Precursor (or redo the restore).

[bunnie]

Thanks for opening this issue! #609 adds an option to reset the backup flag which gives a fix to when you get into this situation, but the actual factory reset procedure should probably also absorb that option. I'll look into this in the next couple of weeks.