ERUSALEM (Reuters) - Israeli and visiting U.S. forces are holding a biennial air-defense exercise this month but on a reduced scale, partly out of reluctance to stoke tensions with Iran, Israeli security sources said on Sunday. hey said the exercise, dubbed Juniper Cobra, this year involves fewer troops and advanced computer simulations -- rather than live-fire drills -- of anti-missile systems such as Israel's Arrow-II and the American-made Patriot PAC-3. "Given the regional situation, especially with Iran, and other factors, we have opted for a much lower profile than previously," an Israeli security source said. Israel and the United States...