Enable gluon multi worker data loader test

[sandeep-krishnamurthy]

Description

Re-enable the skipped test for Gluon DataLoader. Described in this issue - #11455

Tests are working fine on latest master.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:

Changes

• Enable - tests/python/unittest/test_gluon_data.py:test_multi_worker

Comments

Ran for 10,000 runs on CPU/GPU with/without MKLDNN.

~/incubator-mxnet$ MXNET_TEST_COUNT=10000 nosetests -s --verbose tests/python/unittest/test_gluon_data.py:test_multi_worker
/usr/local/lib/python3.5/dist-packages/nose/util.py:453: DeprecationWarning: inspect.getargspec() is deprecated, use inspect.signature() instead
  inspect.getargspec(func)
[INFO] Setting module np/mx/python random seeds, use MXNET_MODULE_SEED=1359342575 to reproduce.
test_gluon_data.test_multi_worker ... ok

----------------------------------------------------------------------
Ran 1 test in 509.370s

OK

@marcoabreu

[sandeep-krishnamurthy]

@marcoabreu - ping.

[marcoabreu]

@piiswrong disable the test. We should check back with him

[sandeep-krishnamurthy]

@piiswrong @marcoabreu - ping.
Can we merge this and see if any issues crop up? In my test runs, I didn't see any failures.

[sandeep-krishnamurthy]

@marcoabreu - I would like to merge this change. As mentioned before, there are no failures in my trail runs. I would revert back / fix if any issues crop up.

[sandeep-krishnamurthy]

@haojin2 - Can you please take a look? Thanks.