spec: Turn on verbose build
    
    When building a package in a build system, such as koji or cbs, logs are
    the only thing which can be used to diagnose failures. Make them verbose
    since human friendly output of V=0 build doesn't really help when a
    build fails.
    
    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
    Reviewed-by: Pino Toscano <ptoscano@redhat.com>