* s3_bucket: fix policy sorting for python3 so strings are evaluated as less than tuples.
Add tests to ensure this behavior is maintained.
* Fix s3_bucket comparison function to work on both Python 3.5 and 3.6
* s3_bucket: document that cmp_to_key is used for python 2.7.
Add another test for s3_bucket to compare policies of different sizes.
* fix pep8
* Work around code-smell grepping by not using the word 'cmp'.
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