Add parameters for selecting by region to command line.

def _add_region_params(region, out_file, items, gatk_type):
    """Add parameters for selecting by region to command line.
    """
    params = []
    variant_regions = bedutils.population_variant_regions(items)
    region = subset_variant_regions(variant_regions, region, out_file, items)
    if region:
        if gatk_type == "gatk4":
            params += ["-L", bamprep.region_to_gatk(region), "--interval-set-rule", "INTERSECTION"]
        else:
            params += ["-L", bamprep.region_to_gatk(region), "--interval_set_rule", "INTERSECTION"]
    params += gatk.standard_cl_params(items)
    return params