Cornerstone Foodservice Group, which already owns Spring USA and Lloyd Pans, added Astra Manufacturing, a Canoga Park, Calif.-based maker of espresso machines and related products for both commercial and residential markets, to its portfolio. The deal was announced Jan. 18. Cornerstone is owned by Minneapolis-based P.E. firm ShoreView Industries. Business Wire: Cornerstone FS Group-Astra Astra…