login: normalize registry-1.docker.io

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

Author: laurazard

cli/command/registry/login.go

@@ -88,7 +88,9 @@ func runLogin(ctx context.Context, dockerCli command.Cli, opts loginOptions) err
 		serverAddress string
 		response      *registrytypes.AuthenticateOKBody
 	)
-	if opts.serverAddress != "" && opts.serverAddress != registry.DefaultNamespace {
+	if opts.serverAddress != "" &&
+		opts.serverAddress != registry.DefaultNamespace &&
+		opts.serverAddress != registry.DefaultRegistryHost {
 		serverAddress = opts.serverAddress
 	} else {
 		serverAddress = registry.IndexServer