Post-process variants, converting into standard VCF file.

def _postprocess_variants(record_file, data, ref_file, out_file):
    """Post-process variants, converting into standard VCF file.
    """
    if not utils.file_uptodate(out_file, record_file):
        with file_transaction(data, out_file) as tx_out_file:
            cmd = ["dv_postprocess_variants.py", "--ref", ref_file,
                   "--infile", record_file, "--outfile", tx_out_file]
            do.run(cmd, "DeepVariant postprocess_variants %s" % dd.get_sample_name(data))
    return out_file