Start the Redis servers.

def start_redis(self):
        """Start the Redis servers."""
        assert self._redis_address is None
        redis_log_files = [self.new_log_files("redis")]
        for i in range(self._ray_params.num_redis_shards):
            redis_log_files.append(self.new_log_files("redis-shard_" + str(i)))

        (self._redis_address, redis_shards,
         process_infos) = ray.services.start_redis(
             self._node_ip_address,
             redis_log_files,
             port=self._ray_params.redis_port,
             redis_shard_ports=self._ray_params.redis_shard_ports,
             num_redis_shards=self._ray_params.num_redis_shards,
             redis_max_clients=self._ray_params.redis_max_clients,
             redirect_worker_output=True,
             password=self._ray_params.redis_password,
             include_java=self._ray_params.include_java,
             redis_max_memory=self._ray_params.redis_max_memory)
        assert (
            ray_constants.PROCESS_TYPE_REDIS_SERVER not in self.all_processes)
        self.all_processes[ray_constants.PROCESS_TYPE_REDIS_SERVER] = (
            process_infos)