We're mired in a "meat grinder" market that may last another six to eight years, David Rosenberg tells CNBC. "The worst stock market since 1937 followed by the best stock market since 1932 followed by the worst May for the Dow since 1940 - there's a word for this type of market. It's called a meat grinder. No return for a decade and yet plenty of sleepless nights on this roller-coaster ride."