Flaky test on MacOS: test_dataset_take

[eric-haibin-lin]

test_gluon_data.test_dataset_take ... ok (0.0002s)
Bug: Gluon DataLoader terminates the process pool early while ... libc++abi.dylib: terminating with uncaught exception of type dmlc::Error: [02:24:07] ../src/storage/./cpu_shared_storage_manager.h:218: Check failed: count >= 0 (-2 vs. 0) : 


/Users/runner/runners/2.168.0/work/_temp/5da477cf-b82d-4965-ae8b-94a3551a8258.sh: line 1: 95004 Abort trap: 6           python3 -m nose --with-timer --verbose tests/python/unittest/ --exclude-test=test_extensions.test_subgraph --exclude-test=test_extensions.test_custom_op --exclude-test=test_gluon_data.test_recordimage_dataset_with_data_loader_multiworker

In PR #17466
https://github.com/apache/incubator-mxnet/pull/17466/checks?check_run_id=559681127

[leezu]

I suspect this is caused by the multiprocessing

2020-04-04T02:24:07.0618480Z test_gluon_data.test_multi_worker ... ok (0.4079s)
2020-04-04T02:24:07.1849230Z test_gluon_data.test_multi_worker_shape ... ok (0.1218s)
2020-04-04T02:24:07.7095350Z test_gluon_data.test_multi_worker_forked_data_loader ... ok (0.5233s)
2020-04-04T02:24:07.7120510Z test_gluon_data.test_multi_worker_dataloader_release_pool ... ok (0.0013s)

They are disabled now as of ff234db

Let's reopen this issue if the error occurs again.