kojibuilder: Pass mergerepo_c --all for bare mode as well.
    
    The '--koji' mode of mergerepo_c implies --all, and thats what we want
    for bare mode as well. The default merge mode is 'repo' which uses the
    first found package by name if multiple packages with the same name are
    in the multiple repos. This causes chaos with rhel8 repos as GA and
    updates content are in the same repo and if it hits an old version of
    one package and an update of another that depends on the new version
    it blows up.
    
    Signed-off-by: Kevin Fenzi <kevin@scrye.com>