cmd/dist, cmd/ctr: move image store access to GRPC

With this changeset, image store access is now moved to completely
accessible over GRPC. No clients manipulate the image store database
directly and the GRPC client is fully featured. The metadata database is
now managed by the daemon and access coordinated via services.

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

cmd/ctr/run.go

@@ -277,27 +277,18 @@ var runCommand = cli.Command{
 			return err
 		}
 
-		db, err := getDB(context, false)
+		imageStore, err := getImageStore(context)
 		if err != nil {
-			return errors.Wrap(err, "failed opening database")
+			return errors.Wrap(err, "failed resolving image store")
 		}
-		defer db.Close()
-
-		tx, err := db.Begin(false)
-		if err != nil {
-			return err
-		}
-		defer tx.Rollback()
 
 		ref := context.Args().First()
 
-		image, err := images.Get(tx, ref)
+		image, err := imageStore.Get(ctx, ref)
 		if err != nil {
 			return errors.Wrapf(err, "could not resolve %q", ref)
 		}
 		// let's close out our db and tx so we don't hold the lock whilst running.
-		tx.Rollback()
-		db.Close()
 
 		diffIDs, err := image.RootFS(ctx, provider)
 		if err != nil {