def _get_instance_list(mig, field='name', filter_list=None):
    """
    Helper to grab field from instances response.

    :param mig: Managed Instance Group Object from libcloud.
    :type mig:  :class: `GCEInstanceGroupManager`

    :param field: Field name in list_managed_instances response.  Defaults
                  to 'name'.
    :type  field: ``str``

    :param filter_list: list of 'currentAction' strings to filter on.  Only
                        items that match a currentAction in this list will
                        be returned.  Default is "['NONE']".
    :type  filter_list: ``list`` of ``str``

    :return: List of strings from list_managed_instances response.
    :rtype: ``list``
    """
    filter_list = ['NONE'] if filter_list is None else filter_list

    return [x[field] for x in mig.list_managed_instances()
            if x['currentAction'] in filter_list]