def combiner_cmd(self):
        raise NotImplementedError
Gets all client_ids for a given list of hostnames or FQDNS.
dataset/ETHPy150Open Yelp/mrjob/mrjob/job.py/MRJob.combiner_cmd--crossover with--dataset/ETHPy150Open google/grr/grr/lib/client_index.py/GetClientURNsForHostnames