List available images for Azure

def avail_images(conn=None, call=None):
    '''
    List available images for Azure
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_images function must be called with '
            '-f or --function, or with the --list-images option'
        )

    if not conn:
        conn = get_conn()

    ret = {}
    for item in conn.list_os_images():
        ret[item.name] = object_to_dict(item)
    for item in conn.list_vm_images():
        ret[item.name] = object_to_dict(item)
    return ret