util: prevent daemon-reload from reaping service processes.

util: prevent daemon-reload from reaping service processes.

The reaping of generator processes run as part of a daemon-reload should not
call waitid(PID_ALL). The waitid() call in execute_directory() is intended only
to reap the executed processes, but if a service process exits at about the
same time as a daemon-reload, then that service process is reaped as well,
preventing it from being reaped in the proper place in
manager_dispatch_sigchld().

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=43625