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/shim_linux.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"os/signal"
+	"syscall"
 
 	"github.com/containerd/containerd/reaper"
 	"github.com/containerd/containerd/sys"
@@ -14,7 +15,7 @@ import (
 // sub-reaper so that the container processes are reparented
 func setupSignals() (chan os.Signal, error) {
 	signals := make(chan os.Signal, 2048)
-	signal.Notify(signals)
+	signal.Notify(signals, syscall.SIGTERM, syscall.SIGINT, syscall.SIGCHLD)
 	// make sure runc is setup to use the monitor
 	// for waiting on processes
 	runc.Monitor = reaper.Default