Fix shim deadlock when joining an existing pid namespace (#290)

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

supervisor/delete.go

@@ -14,6 +14,7 @@ type DeleteTask struct {
 	Status  int
 	PID     string
 	NoEvent bool
+	Process runtime.Process
 }
 
 func (s *Supervisor) delete(t *DeleteTask) error {
@@ -22,6 +23,9 @@ func (s *Supervisor) delete(t *DeleteTask) error {
 		if err := s.deleteContainer(i.container); err != nil {
 			logrus.WithField("error", err).Error("containerd: deleting container")
 		}
+		if t.Process != nil {
+			t.Process.Wait()
+		}
 		if !t.NoEvent {
 			s.notifySubscribers(Event{
 				Type:      StateExit,