Support for resuming from any update state after a spontaneous reboot

Acceptance criteria:

• Implement Update Module API which will ask the Update Module whether it supports resuming from any state
• For modules that do, restart execution at last unfinished state
• Modules that don't must still fail the update, as before (feature is opt-in)
• TBD: What to do about State transition counter (StateDataStoreCount).
  • Without it we will not be able to break out of reboot loops and the client will be stuck forever.
  • OTOH it does not fit well with long running updates that are constantly postponed. In this scenario we may have dozens, maybe hundreds of reboots before the update is finally applied.