Fixed duplicate oauth fetch along with DRY improvement #1858

Fixes the duplicate Oauth issue.
In theory I agree with that, but in practice I don't think it makes any difference because there's no way for GoogleOauth2CallbackServlet and OauthUtils to collide. The problem with adding something like OAuthInfo is that it would break compatibility with old clients and would force everyone to log in again (unless we did some gymnastics to handle that case, but that seems overly complicated).