Update systemService apt monitoring

[MorningLightMountain713]

What this pull does

• Simplifies aptMonitoring logic. We no longer wait for 12 hours and resume the apt queue if there is a failure. We just empty the queue and start fresh. resuming after 12 hours didn't make sense - the commands would be stale by then anyway.
• We now gracefully, then forcefully terminate ANY process that holds a lock on the apt locks. This uses fuser in combindation with -k -TERM to gracefully ask the processes to quit, followed by -k -KILL if that fails. This is good as it looks at what processes are holding the locks on the actual files, not just killing off apt or apt-get.
• Fix up tests related to the above changes.
• Remove some old code from syncthing that was no longer used as of 5.6.0.
• Rename some fifo queue variables that didn't make sense.

I've tested this on a live node by doing the following:

• Downgrade syncthing to 1.27.5.
• Run sudo apt-get remove syncthing but don't press y or n, so it hangs.
• Reboot FluxOS, so it tries to install syncthing.
• Apt Queue Does the following:
  • 3 minutes for initial try.
  • 5 retries @ 3 minutes.
  • 1 minute between retries ( 5 minutes)
  • Total of 23 minutes
• Monitor apt queue then does:
  • 3 checks @ 10 minutes.
  • Total 30 minutes
  • Kills any processes that hold locks
• Total time to resolve 53 minutes.

If this was run on a node that didn't have a newer version of apt, would take 35 minutes before the processes are killed.

All tests passing.

[Cabecinha84]

Ack. Great work