Add s3 integration tests using directory buckets

[hssyoo]

Set up S3 directory bucket creation/teardown for integration tests with high-level s3 commands. For the existing teardown logic to be compatible with directory buckets, we switch from ListObjects to ListObjectsV2 when clearing out test buckets.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 26 lines in your changes missing coverage. Please review.

Project coverage is 0.08%. Comparing base (489efff) to head (f67b9ec).
Report is 45 commits behind head on develop.

Files	Patch %	Lines
awscli/testutils.py	0.00%	26 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #8795      +/-   ##
==========================================
- Coverage     0.08%   0.08%   -0.01%     
==========================================
  Files          210     210              
  Lines        16908   16933      +25     
==========================================
  Hits            14      14              
- Misses       16894   16919      +25     

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[kdaily]

Looks good overall, a couple minor things. just around some naming consistency.