Add runtimeArgs to pass to shim

This allows you to pass options like:

```bash
containerd --debug --runtime-args "--debug" --runtime-args
"--systemd-cgroup"
```

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

containerd/main.go

@@ -50,6 +50,11 @@ var daemonFlags = []cli.Flag{
 		Value: "runc",
 		Usage: "name of the OCI compliant runtime to use when executing containers",
 	},
+	cli.StringSliceFlag{
+		Name:  "runtime-args",
+		Value: &cli.StringSlice{},
+		Usage: "specify additional runtime args",
+	},
 }
 
 func main() {
@@ -71,6 +76,7 @@ func main() {
 			context.String("state-dir"),
 			10,
 			context.String("runtime"),
+			context.StringSlice("runtime-args"),
 		); err != nil {
 			logrus.Fatal(err)
 		}
@@ -80,7 +86,7 @@ func main() {
 	}
 }
 
-func daemon(address, stateDir string, concurrency int, runtimeName string) error {
+func daemon(address, stateDir string, concurrency int, runtimeName string, runtimeArgs []string) error {
 	// setup a standard reaper so that we don't leave any zombies if we are still alive
 	// this is just good practice because we are spawning new processes
 	s := make(chan os.Signal, 2048)
@@ -88,7 +94,7 @@ func daemon(address, stateDir string, concurrency int, runtimeName string) error
 	if err := osutils.SetSubreaper(1); err != nil {
 		logrus.WithField("error", err).Error("containerd: set subpreaper")
 	}
-	sv, err := supervisor.New(stateDir, runtimeName)
+	sv, err := supervisor.New(stateDir, runtimeName, runtimeArgs)
 	if err != nil {
 		return err
 	}