When exiting, let's explicitly wait for our worker processes to finish
first. That's useful if unmounting of /home/ is scheduled to happen
right after homed is down, as we then can be sure that the home
directories are properly unmounted and detached by the time homed is
fully terminated (otherwise it might happen that our worker gets killed
by the service manager, thus leaving the home directory and its backing
devices up/left for auto-clean which might be async).
Likely fixes#16842
"home" is okay-ish in English, but rather awkward in many other languages.
For example, even before this change, in fr.po we had "un espace personnel"
as the translation everywhere. Let's use a less overloaded term.
Fixes#14789.
Lennart Poettering