Only allow single container operation

As per the discussions in #1156 , we think it's a bad
idea to allow multi container operations in runc. So
revert it.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>

start.go

@@ -1,8 +1,8 @@
 package main
 
 import (
+	"errors"
 	"fmt"
-	"os"
 
 	"github.com/opencontainers/runc/libcontainer"
 	"github.com/urfave/cli"
@@ -11,56 +11,33 @@ import (
 var startCommand = cli.Command{
 	Name:  "start",
 	Usage: "executes the user defined process in a created container",
-	ArgsUsage: `<container-id> [container-id...]
+	ArgsUsage: `<container-id>
 
 Where "<container-id>" is your name for the instance of the container that you
 are starting. The name you provide for the container instance must be unique on
 your host.`,
-	Description: `The start command executes the user defined process in a created container .`,
+	Description: `The start command executes the user defined process in a created container.`,
 	Action: func(context *cli.Context) error {
-		if err := checkArgs(context, 1, minArgs); err != nil {
+		if err := checkArgs(context, 1, exactArgs); err != nil {
 			return err
 		}
-		hasError := false
-		factory, err := loadFactory(context)
+		container, err := getContainer(context)
 		if err != nil {
 			return err
 		}
-
-		for _, id := range context.Args() {
-			container, err := factory.Load(id)
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "container %s does not exist\n", id)
-				hasError = true
-				continue
-			}
-			status, err := container.Status()
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "status for %s: %v\n", id, err)
-				hasError = true
-				continue
-			}
-			switch status {
-			case libcontainer.Created:
-				if err := container.Exec(); err != nil {
-					fmt.Fprintf(os.Stderr, "start for %s failed: %v\n", id, err)
-					hasError = true
-				}
-			case libcontainer.Stopped:
-				fmt.Fprintln(os.Stderr, "cannot start a container that has stopped")
-				hasError = true
-			case libcontainer.Running:
-				fmt.Fprintln(os.Stderr, "cannot start an already running container")
-				hasError = true
-			default:
-				fmt.Fprintf(os.Stderr, "cannot start a container in the %s state\n", status)
-				hasError = true
-			}
+		status, err := container.Status()
+		if err != nil {
+			return err
 		}
-
-		if hasError {
-			return fmt.Errorf("one or more of container start failed")
+		switch status {
+		case libcontainer.Created:
+			return container.Exec()
+		case libcontainer.Stopped:
+			return errors.New("cannot start a container that has stopped")
+		case libcontainer.Running:
+			return errors.New("cannot start an already running container")
+		default:
+			return fmt.Errorf("cannot start a container in the %s state\n", status)
 		}
-		return nil
 	},
 }