Rework fedup --reboot etc.

[wgwoods]

It would make a lot more sense if we didn't touch your bootloader config automatically. Instead it should work kind of like git rebase --interactive:

# fedup --network 21
<chug chug chug, interrupted>
# fedup --status
Downloading data for 'fedup --network 21'.
Try 'fedup --continue' to continue upgrade, or 'fedup --abort' to clean up.
# fedup --continue
<chug chug>
All done. Use 'fedup --reboot' to start upgrade.
# fedup --reboot