By Jill SerjeantLOS ANGELES (Reuters) - Courtroom drama "The Trial of the Chicago 7" and jazz period film "Ma Rainey's Black Bottom" were the big winners at the Screen Actors Guild (SAG) awards, one of the last major ceremonies before the Oscars. "The Trial of the Chicago 7," set during a Vietnam War protest in 1968, took the prize for best ensemble with a cast that includes Sacha Baron Cohen, Eddie Redmayne, Frank Langella and Mark Rylance.