'List cluster steps
:type cluster_id: str
:param cluster_id: The cluster id of interest
:type step_states: list
:param step_states: Filter by step states
:type marker: str
:param marker: Pagination marker'

def list_steps(self, cluster_id, step_states=None, marker=None):

    params = {'ClusterId': cluster_id}
    if marker:
        params['Marker'] = marker
    if step_states:
        self.build_list_params(params, step_states, 'StepStates.member')
    return self.get_object('ListSteps', params, StepSummaryList)
