Creates clusterState by iterating over all k8s pods with the label
`app=teraslice`
@constructor
@return      {Promise} [description]
function _getClusterState() {
        return k8s.list('app=teraslice', 'pods')
            .then(k8sPods => k8sState.gen(k8sPods, clusterState, clusterNameLabel))
            .catch((err) => {
                // TODO: We might need to do more here.  I think it's OK to just
                // log though.  This only gets used to show slicer info through
                // the API.  We wouldn't want to disrupt the cluster master
                // for rare failures to reach the k8s API.
                logger.error(err, 'Error listing teraslice pods in k8s');
            });
    }