Comment 47 for bug 1840122

Actually there may be an even better solution:

   Before=shutdown.target

which lintian has been nagging us about:

  https://lintian.debian.org/tags/systemd-service-file-shutdown-problems

"There is race condition between stopping units and systemd getting a request to exit the main loop, so it may proceed with shutdown before all pending stop jobs have been processed."