Retrieve full list of values for the contentkey from a boto3 ApiGateway
    client function that may be paged via 'position'

def _multi_call(function, contentkey, *args, **kwargs):
    '''
    Retrieve full list of values for the contentkey from a boto3 ApiGateway
    client function that may be paged via 'position'
    '''
    ret = function(*args, **kwargs)
    position = ret.get('position')

    while position:
        more = function(*args, position=position, **kwargs)
        ret[contentkey].extend(more[contentkey])
        position = more.get('position')
    return ret.get(contentkey)