List available images for OpenStack

    CLI Example

    .. code-block:: bash

        salt-cloud -f avail_images myopenstack
        salt-cloud --list-images myopenstack

def avail_images(conn=None, call=None):
    '''
    List available images for OpenStack

    CLI Example

    .. code-block:: bash

        salt-cloud -f avail_images myopenstack
        salt-cloud --list-images myopenstack

    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_images function must be called with '
            '-f or --function, or with the --list-images option'
        )
    if conn is None:
        conn = get_conn()
    return conn.list_images()