Do work of preparing BAM input file on the selected region.

def _piped_bamprep_region(data, region, out_file, tmp_dir):
    """Do work of preparing BAM input file on the selected region.
    """
    if _need_prep(data):
        prep_params = _get_prep_params(data)
        _piped_bamprep_region_gatk(data, region, prep_params, out_file, tmp_dir)
    else:
        raise ValueError("No realignment specified")