Aws sdk v2

* Added s3 storage implementation using the aws-sdk v2.

There are still a few things that need fixing (see pending specs):
* Flaky specs. Is this due to the v2 stubbing?
* s3_host_name - should it be replaced s3_region
* Figure out credential_provider spec.
* Some spec tests SlowDown exception which where a v1 concept.

Unused block argument - `headers`. If it's necessary, use `_` or `_headers` as an argument name to indicate that it won't be used.<br>Prefer `reduce` over `inject`.<br>Space missing after comma.