Add ContainerService.Info to get info about a single container

For clients which only want to know about one container this is simpler than
searching the result of execution.List.

Signed-off-by: Ian Campbell <ian.campbell@docker.com>

cmd/ctr/info.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"encoding/json"
+
+	gocontext "context"
+	"fmt"
+
+	"github.com/docker/containerd/api/services/execution"
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+var infoCommand = cli.Command{
+	Name:  "info",
+	Usage: "get info about a container",
+	Flags: []cli.Flag{
+		cli.StringFlag{
+			Name:  "id",
+			Usage: "id of the container",
+		},
+	},
+	Action: func(context *cli.Context) error {
+		id := context.String("id")
+		if id == "" {
+			return errors.New("container id must be provided")
+		}
+
+		containers, err := getExecutionService(context)
+		if err != nil {
+			return err
+		}
+		response, err := containers.Info(gocontext.Background(), &execution.InfoRequest{ID: id})
+		if err != nil {
+			return err
+		}
+		json, err := json.MarshalIndent(response, "", "    ")
+		if err != nil {
+			return err
+		}
+		fmt.Println(string(json))
+		return nil
+	},
+}