Chris Willman Senior Music Writer and Chief Music CriticNot since Kanye and Drake played the Coliseum together six months ago has there been a coming together of forces quite so opposite on a stage in Los Angeles, or maybe anywhere. We’re speaking, of course, of the combined performance by the UCLA and USC marching bands (mentioned here in alphabetical order — no favoritism) that climaxed the official opening of the Hollywood Bowl’s summer season Friday night.It takes a lot to overshadow Gwen Stefani, the LA Phil, Gwen Stefani with the LA Phil, a pair of world-class ballet dancers, Branford Marsalis performing the film music of John Williams, and Williams making a surprise appearance to conduct his own world-premiere piece.