Transfer: Registry: Enable to use registry configuration diretory

Currently transfer service isn't aware of configurations of hosts directory and
ctr's `--hosts-dir` doesn't work.
This commit fixes this issue by using `config.ConfigureHosts` instead of
`docker.ConfigureDefaultRegistries`.
This commit also fixes ctr to use this feature for "--hosts-dir" flag.

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

cmd/ctr/commands/images/pull.go

@@ -132,7 +132,10 @@ command. As part of this process, we do the following:
 				sopts = append(sopts, image.WithAllMetadata)
 			}
 
-			reg := registry.NewOCIRegistry(ref, nil, ch)
+			reg, err := registry.NewOCIRegistry(ctx, ref, registry.WithCredentials(ch), registry.WithHostDir(context.String("hosts-dir")))
+			if err != nil {
+				return err
+			}
 			is := image.NewStore(ref, sopts...)
 
 			pf, done := ProgressHandler(ctx, os.Stdout)

cmd/ctr/commands/images/push.go

@@ -104,7 +104,10 @@ var pushCommand = &cli.Command{
 			if local == "" {
 				local = ref
 			}
-			reg := registry.NewOCIRegistry(ref, nil, ch)
+			reg, err := registry.NewOCIRegistry(ctx, ref, registry.WithCredentials(ch), registry.WithHostDir(context.String("hosts-dir")))
+			if err != nil {
+				return err
+			}
 			is := image.NewStore(local)
 
 			pf, done := ProgressHandler(ctx, os.Stdout)