rpm: Switch to new macros for handling of systemd units

rpm: Switch to new macros for handling of systemd units

In most cases the replacement is straightforward, with the
biggest difference being that we now schedule restarts during
%pre instead of %post. This also means that we can get rid of
%post for most packages, reducing the number of scriptlets that
need to run during install/upgrade.

Notable exceptions are libvirt-guests.service, where we stop
using the standard systemd macros to adopt our custom ones, as
well as the virtlogd and virtlockd services, where the reload
operation is moved from %postun to %posttrans.

https://bugzilla.redhat.com/show_bug.cgi?id=2210058

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>