Return a dict of all available VM images on the cloud provider.

def avail_images(call=None):
    '''
    Return a dict of all available VM images on the cloud provider.
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_images function must be called with '
            '-f or --function, or with the --list-images option'
        )

    ret = {}
    conn = get_conn()
    response = conn.getCreateObjectOptions()
    for image in response['operatingSystems']:
        ret[image['itemPrice']['item']['description']] = {
            'name': image['itemPrice']['item']['description'],
            'template': image['template']['operatingSystemReferenceCode'],
        }
    return ret