linux: Ensure all init children are dead when it exits

This ensure that when using the host pid, we don't let process alive,
preventing Wait() to return until they all die.

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

linux/shim/service.go

@@ -393,6 +393,14 @@ func (s *Service) checkProcesses(e runc.Exit) {
 	defer s.mu.Unlock()
 	for _, p := range s.processes {
 		if p.Pid() == e.Pid {
+			if ip, ok := p.(*initProcess); ok {
+				// Ensure all children are killed
+				if err := ip.killAll(s.context); err != nil {
+					log.G(s.context).WithError(err).WithField("id", ip.ID()).
+						Error("failed to kill init's children")
+				}
+			}
+
 			p.SetExited(e.Status)
 			s.events <- &eventsapi.TaskExit{
 				ContainerID: s.id,