'This method determines whether to terminate the cluster based on the
following conditions:
1. Only the master node exists (no worker nodes)
2. The master node is not running any SGE jobs
3. The master node has been up for at least self.kill_after mins'

def _eval_terminate_cluster(self):

    if (len(self._cluster.running_nodes) != 1):
        return False
    return self._should_remove(self._cluster.master_node)
