Calculate structural variant bins using target/anti-target approach from CNVkit.

def _calculate_sv_bins_cnvkit(data, cnv_group, size_calc_fn):
    """Calculate structural variant bins using target/anti-target approach from CNVkit.
    """
    from bcbio.structural import cnvkit
    if dd.get_background_cnv_reference(data, "cnvkit"):
        target_bed, anti_bed = cnvkit.targets_from_background(dd.get_background_cnv_reference(data, "cnvkit"),
                                                              cnv_group.work_dir, data)
    else:
        target_bed, anti_bed = cnvkit.targets_w_bins(cnv_group.region_file, cnv_group.access_file,
                                                     size_calc_fn, cnv_group.work_dir, data)
    return target_bed, anti_bed, None