Return exit status from Wait of stopped process

This changes Wait() from returning an error whenever you call wait on a
stopped process/task to returning the exit status from the process.

This also adds the exit status to the Status() call on a process/task so
that a user can Wait(), check status, then cancel the wait to avoid
races in event handling.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/ctr/delete.go

@@ -59,7 +59,7 @@ func deleteContainer(ctx context.Context, client *containerd.Client, id string,
 	if err != nil {
 		return err
 	}
-	if status == containerd.Stopped || status == containerd.Created {
+	if status.Status == containerd.Stopped || status.Status == containerd.Created {
 		if _, err := task.Delete(ctx); err != nil {
 			return err
 		}