Add DefaultAddress to client

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

cmd/ctr/main.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/Sirupsen/logrus"
+	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/version"
 	"github.com/urfave/cli"
 )
@@ -38,7 +39,7 @@ containerd CLI
 		cli.StringFlag{
 			Name:  "address, a",
 			Usage: "address for containerd's GRPC server",
-			Value: "/run/containerd/containerd.sock",
+			Value: containerd.DefaultAddress,
 		},
 		cli.DurationFlag{
 			Name:  "timeout",