'Adds instance groups to a running cluster.
:type jobflow_id: str
:param jobflow_id: The id of the jobflow which will take the
new instance groups
:type instance_groups: list(boto.emr.InstanceGroup)
:param instance_groups: A list of instance groups to add to the job'

def add_instance_groups(self, jobflow_id, instance_groups):

    if (not isinstance(instance_groups, list)):
        instance_groups = [instance_groups]
    params = {}
    params['JobFlowId'] = jobflow_id
    params.update(self._build_instance_group_list_args(instance_groups))
    return self.get_object('AddInstanceGroups', params, AddInstanceGroupsResponse, verb='POST')
