Switch to event based timer
Switch from a calendar based timer to an event based timer for the leap second download service. This will ensure that the initial download of a leap second file happens soon after the timer service is started, whereas the current calendar based timer will wait up to a week before the first run. This also avoids the need to have an extra manual 'systemctl start ietf-leap-seconds' invocation after enabling the timer, or the need to embed such a call in the %postinstall section of a kickstart file (where network access is not necessarily assured).
See commit 3880d145 for a proposed fix.