cmd/dist: port commands over to use GRPC content store

Following from the rest of the work in this branch, we now are porting
the dist command to work directly against the containerd content API.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

cmd/dist/get.go

@@ -4,6 +4,8 @@ import (
 	"io"
 	"os"
 
+	contentapi "github.com/docker/containerd/api/services/content"
+	"github.com/docker/containerd/content"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/urfave/cli"
 )
@@ -17,17 +19,23 @@ var getCommand = cli.Command{
 Output paths can be used to directly access blobs on disk.`,
 	Flags: []cli.Flag{},
 	Action: func(context *cli.Context) error {
-		cs, err := resolveContentStore(context)
-		if err != nil {
-			return err
-		}
+		var (
+			ctx = background
+		)
 
 		dgst, err := digest.Parse(context.Args().First())
 		if err != nil {
 			return err
 		}
 
-		rc, err := cs.Open(dgst)
+		conn, err := connectGRPC(context)
+		if err != nil {
+			return err
+		}
+
+		cs := content.NewProviderFromClient(contentapi.NewContentClient(conn))
+
+		rc, err := cs.Reader(ctx, dgst)
 		if err != nil {
 			return err
 		}