main/ifupdown-ng: backport fix to stop running executors after one fails
Without these patches, all executors of a given phase will be executed even if one of them fails. This has been bugging me for a while and is especially annoying in conjunction with ifupdown-ng-waitif. I proposed fixing this upstream two years ago (and it has indeed been fixed) but since there hasn't been a new release since I would like to backport this for now.