This commit changes a lot more that you'd expect but it also adds a lot
of new testing code so nothing breaks in the future. The main change is
that sockets are now restarted when they change. The main reason for
the large amount of changes is the ability of activation scripts to
restart/reload units. This also works for socket-activated units now,
and honors reloadIfChanged and restartIfChanged. The two changes don't
really work without each other so they are done in the one large commit.
The test should show what works now and ensure it will continue to do so
in the future.
The `| tee` invocation always masked the return value of the
switch-to-configuration test.
```
~ $ false | tee && echo "oh no"
oh no
```
The added wrapper script will still output everything to stderr, while
passing failures to the test harness.
Fixes #28443
Fixed few invocations to `systemctl` to have an absolute path. Additionally add
LOCALE_ARCHIVE so that perl stops spewing warning messages.
