List subnets in a virtual network

    network
        network to list subnets of

    .. code-block:: bash

        salt-cloud -f list_subnets myopenstack network=salt-net

def list_subnets(conn=None, call=None, kwargs=None):
    '''
    List subnets in a virtual network

    network
        network to list subnets of

    .. code-block:: bash

        salt-cloud -f list_subnets myopenstack network=salt-net

    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The list_subnets function must be called with '
            '-f or --function.'
        )
    if conn is None:
        conn = get_conn()
    if kwargs is None or (isinstance(kwargs, dict) and 'network' not in kwargs):
        raise SaltCloudSystemExit(
            'A `network` must be specified'
        )
    return conn.list_subnets(filters={'network': kwargs['network']})