The end year is legally and functionally redundant, and more importantly causes
cherry-pick conflicts when trying to maintain old branches. Use git for history.
In 1de7cc we checked the version format when checking for update, but there are
many other places that are doing verfmt-insensitive comparisons. For instance,
the predicates in <requires> all fail if the device version format is plain.
his breaks updating some NVMe drives where the `ne` requirements are not
semantic versions.
To avoid trying to catch all the bugs in different places, and in case we have
a future verfmt that should be treated another way, refactor this out in to a
common function and deprecate the old function.
Older versions of Plymouth are more fragile and we can sometimes block the
offline process waiting for the splash to appear.
Use the new system-upgrade and reboot modes, falling back to older modes if
unavailable, showing text on stderr if Plymouth is either not installed or just
not working.
We've already done the permissions check in the scheduler, and allowing
downgrade allows the user to go back to a working version in the event of a
regression.
The offline updates environment is special, and we have to be careful to delete
the trigger before doing anything that can fail to avoid boot loops.
For this reason, split it out to a simple self-contained binary that is easy to
understand.
