Re-enabling randomized test_l2_normalization

[haojin2]

Description

test_l2_normalization should be no more flaky, getting rid of the fixed seed.

Checklist

Essentials

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• Getting rid of fixed seed
• Refactor the test to make it randomized and shorter

Comments

Can pass more than 10000 times in total counting both CPU & GPU

MXNET_TEST_COUNT=5000 nosetests -s --verbose tests/python/unittest/test_operator.py:test_l2_normalization
/home/ubuntu/anaconda3/lib/python3.6/site-packages/nose/util.py:453: DeprecationWarning: inspect.getargspec() is deprecated, use inspect.signature() or inspect.getfullargspec()
  inspect.getargspec(func)
[INFO] Setting module np/mx/python random seeds, use MXNET_MODULE_SEED=2133892746 to reproduce.
test_operator.test_l2_normalization ... ok

----------------------------------------------------------------------
Ran 1 test in 8377.651s

OK

MXNET_TEST_COUNT=5000 nosetests -s --verbose tests/python/gpu/test_operator_gpu.py:test_l2_normalization
/home/ubuntu/anaconda3/lib/python3.6/site-packages/urllib3/contrib/pyopenssl.py:46: DeprecationWarning: OpenSSL.rand is deprecated - you should use os.urandom instead
  import OpenSSL.SSL
/home/ubuntu/anaconda3/lib/python3.6/site-packages/nose/util.py:453: DeprecationWarning: inspect.getargspec() is deprecated, use inspect.signature() or inspect.getfullargspec()
  inspect.getargspec(func)
[INFO] Setting module np/mx/python random seeds, use MXNET_MODULE_SEED=1517428789 to reproduce.
test_operator_gpu.test_l2_normalization ... ok

----------------------------------------------------------------------
Ran 1 test in 14675.545s

OK

[haojin2]

Should fix #11717

[haojin2]

@marcoabreu

[rahul003]

Was this seed added before the fp16 support for this operator?

[haojin2]

@rahul003 lemme have a check...

[haojin2]

@rahul003 It was added before my PR for support for fp16 merged: https://github.com/apache/incubator-mxnet/blame/master/tests/python/unittest/test_operator.py#L3021