List available sizes for OpenStack

    CLI Example

    .. code-block:: bash

        salt-cloud -f avail_sizes myopenstack
        salt-cloud --list-sizes myopenstack

def avail_sizes(conn=None, call=None):
    '''
    List available sizes for OpenStack

    CLI Example

    .. code-block:: bash

        salt-cloud -f avail_sizes myopenstack
        salt-cloud --list-sizes myopenstack

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