GLOBAL MARKETS-Oil, weak German data drag on stocks; Brazil sinks

* Wall St lower, hit as oil falls* Brent crude trades near four-year lows* Optimism around ECB stress tests is short-lived* German Ifo index falls to lowest in almost 2 years(Recasts with U.S. open, new quote, falling oil prices; changes dateline; previous LONDON)By Yasmeen AbutalebNEW YORK, Oct 27 (Reuters) - Global equity markets slipped on Monday, hit by weak German business sentiment and anoth