Concerns about the financial impact of a spate of class-action lawsuits has led Moody’s Investors Service to downgrade the servicer rating of Ocwen Federal Bank. But the rating agency generally had good things to say about Ocwen, which is a major servicer of subprime mortgages, managing a portfolio totaling $37.7 billion at the end of December.While lowering Ocwen’s rating from SQ1 – its highest grade – to SQ2, Moody’s