Installer: Clean up RepoIO interface

Change-Id: If80d7be1460c725b7df9d1d27c9354cb9141acfe
diff --git a/core/installer/cmd/welcome.go b/core/installer/cmd/welcome.go
index 43578b2..4390fcf 100644
--- a/core/installer/cmd/welcome.go
+++ b/core/installer/cmd/welcome.go
@@ -80,13 +80,17 @@
 	if err != nil {
 		return err
 	}
+	repoIO, err := installer.NewRepoIO(repo, signer)
+	if err != nil {
+		return err
+	}
 	nsCreator, err := newNSCreator()
 	if err != nil {
 		return err
 	}
 	s := welcome.NewServer(
 		welcomeFlags.port,
-		installer.NewRepoIO(repo, signer),
+		repoIO,
 		nsCreator,
 		welcomeFlags.createAccountAddr,
 		welcomeFlags.loginAddr,