rpm: restart services in %posttrans

This fixes a long-standing issue in packaging scriptlets: daemon-reload
was moved to the end of the transaction, but restarting services was still
straightaway after package installation.

https://bugzilla.redhat.com/show_bug.cgi?id=1614751

Note that daemon-reload is called twice. This wouldn't be hardly noticable,
except that now a bunch of units (at least in Fedora) generate very verbose
warnings about deprecated features. So we get those warnings twice…

reload-or-restart --needing-restart is also called twice, but the second call
is usually a noop, because the first clears the flag for restarted units. The
second call is necessary for the case where we only uninstall packages, and the
%transfiletriggerpostun trigger fires, but not the %transfiletriggerin
scriptlet.

Also note that this assumes that units are marked only for restart if paths
under @systemunitdir@ or /etc/systemd/system have been touched. I would prefer
make the trigger that does 'restart --needing-restart' fire always, but it
seems rpm doesn't have such functionality. (Except as a %transfiletrigger that
would trigger on "/*" to catch all transactions, but that seems ineffiecient
and ugly.)