Fix exit event handling in shim

Could issues where when exec processes fail the wait block is not
released.

Second, you could not dump stacks if the reaper loop locks up.

Third, the publisher was not waiting on the correct pid.

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

cmd/containerd-shim/main_unix.go

@@ -11,6 +11,7 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"os/signal"
 	"runtime"
 	"strings"
 	"sync"
@@ -80,6 +81,9 @@ func executeShim() error {
 	if err != nil {
 		return err
 	}
+	dump := make(chan os.Signal, 32)
+	signal.Notify(dump, syscall.SIGUSR1)
+
 	path, err := os.Getwd()
 	if err != nil {
 		return err
@@ -111,6 +115,11 @@ func executeShim() error {
 		"path":      path,
 		"namespace": namespaceFlag,
 	})
+	go func() {
+		for range dump {
+			dumpStacks(logger)
+		}
+	}()
 	return handleSignals(logger, signals, server, sv)
 }
 
@@ -171,8 +180,6 @@ func handleSignals(logger *logrus.Entry, signals chan os.Signal, server *ttrpc.S
 					sv.Delete(context.Background(), &ptypes.Empty{})
 					close(done)
 				})
-			case unix.SIGUSR1:
-				dumpStacks(logger)
 			}
 		}
 	}
@@ -213,8 +220,11 @@ func (l *remoteEventsPublisher) Publish(ctx context.Context, topic string, event
 	if err != nil {
 		return err
 	}
-	exit := <-c
-	if exit.Status != 0 {
+	status, err := reaper.Default.Wait(cmd, c)
+	if err != nil {
+		return err
+	}
+	if status != 0 {
 		return errors.New("failed to publish event")
 	}
 	return nil