Integrate sys.SetSubreaper, sys.GetSubreaper in sys/reaper package

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/containerd-shim/shim_linux.go

@@ -20,7 +20,6 @@ import (
 	"os"
 	"os/signal"
 
-	"github.com/containerd/containerd/sys"
 	"github.com/containerd/containerd/sys/reaper"
 	runc "github.com/containerd/go-runc"
 	"github.com/containerd/ttrpc"
@@ -36,7 +35,7 @@ func setupSignals() (chan os.Signal, error) {
 	// for waiting on processes
 	runc.Monitor = reaper.Default
 	// set the shim as the subreaper for all orphaned processes created by the container
-	if err := sys.SetSubreaper(1); err != nil {
+	if err := reaper.SetSubreaper(1); err != nil {
 		return nil, err
 	}
 	return signals, nil