In Justice League: DOOM, there was a character named Ackerson, Metallo either killed him or something to take his place and lured Superman to the Daily Planet to fulfill his part of Vandal Savage's plan.
Metallo in that movie was never actually called "John Corben" but I do think someone called him "John" in one scene.
As for Man Of Steel, it's possible their only calling him that now to throw ppl off, and in the movie itself he is named Corben, probably will be in the military, similar to his part in Superman: Secret Origin, I say that cause yes I know he was in the military as well in the new 52 stuff, but the script for Man Of Steel was made and filmed before Corben showed up in the new 52