DEVPROD-17135 Use the AWS-sdk for accessing the s3 bucket of test statistics

[sleaux]

This replaces the manual requests to the s3 endpoint of test statistics with the AWS-sdk. This, in addition to limiting concurrent connections, dramatically improves the reliability of retrieving test stats.

[sleaux]

Typically, one version_gen task fails to get the test stats for 100-200 tasks. In testing this in combination with #95, this is reduced to zero.

I didn't expect to have to fix so many lint issues that they would obscure the review. The real meat of the change is in the second commit, 9994a78.