If we bundle the driver to cqlsh using the 3.6.0 tag or cassandra_test head, some cqlsh copy tests hang, for example test_bulk_round_trip_blogposts. See CASSANDRA-12736 and CASSANDRA-11534 for some sample failures.
If the driver fails to invoke a callback (either error or success), or if the server never answers to the driver, then the copy parent process will wait forever to receive an answer from child processes. We should put a cap to this. We should also use a very high timeout rather than None, so that the driver will notify us if there is no answer from the server.