build a soapenc:Array made of ints called `el_name` as a child
    of `parent`

def _build_int_array_el(el_name, parent, list_):
    """build a soapenc:Array made of ints called `el_name` as a child
    of `parent`"""
    el = parent.add_child(el_name)
    el.add_attribute('xmlns:soapenc',
                     'http://schemas.xmlsoap.org/soap/encoding/')
    el.add_attribute('xsi:type', 'soapenc:Array')
    el.add_attribute('soapenc:arrayType', 'xsd:int[{:d}]'.format(len(list_)))
    for item in list_:
        item_el = el.add_child('item', str(item))
        item_el.add_attribute('xsi:type', 'xsd:int')
    return el