'Returns a list of existing clusters.
:type next_token: string
:param next_token: The `nextToken` value returned from a previous
paginated `ListClusters` request where `maxResults` was used and
the results exceeded the value of that parameter. Pagination
continues from the end of the previous results that returned the
`nextToken` value. This value is `null` when there are no more
results to return.
:type max_results: integer
:param max_results: The maximum number of cluster results returned by
`ListClusters` in paginated output. When this parameter is used,
`ListClusters` only returns `maxResults` results in a single page
along with a `nextToken` response element. The remaining results of
the initial request can be seen by sending another `ListClusters`
request with the returned `nextToken` value. This value can be
between 1 and 100. If this parameter is not used, then
`ListClusters` returns up to 100 results and a `nextToken` value if
applicable.'

def list_clusters(self, next_token=None, max_results=None):

    params = {}
    if (next_token is not None):
        params['nextToken'] = next_token
    if (max_results is not None):
        params['maxResults'] = max_results
    return self._make_request(action='ListClusters', verb='POST', path='/', params=params)
