s4: process_prefork: Make prefork_restart() use an asynchronous timer event instead...

s4: process_prefork: Make prefork_restart() use an asynchronous timer event instead of calling sleep(X).

This should prevent any long pauses in the calling process, as we get a callback
for the restart after X seconds. To make the code flow more understandable,
always go through a timer event even if the wait time is zero. This
has the same effect as an immediate event as it will call the callback
function as soon as we go back into the event loop.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Oct  2 01:38:43 UTC 2021 on sn-devel-184