* cosmetic: Remove useless call to ec2_argument_spec()
* aws_s3: Improve ETag handling
* Extract ETag calculation into a utility function for reuse by
aws_s3_sync.
* Reduce code duplication in put/get by restructuring the logic
* Only calculate ETag when overwrite == different
* Fail gracefully when overwrite == different and MD5 isn't available
(e.g. due to FIPS-140-2).
* aws_s3: clean up integration tests
Clean up tests, add tests for overwrite settings in both directions.
c513c1e2d3