Fixes unit specs due to signing version logic change
Fixes unit specs due to signing version logic change

We updated the core logic to essentially prefer v4 signing using
integration tests but forgot to update the unit tests as well

[#108585160](https://www.pivotaltracker.com/story/show/108585160)

Signed-off-by: Jonathan Barnes <bc7add126c2dbb8382bf1c28ac262b9363a32706@pivotal.io>

pivotal-golang/s3cli,pivotal-golang/s3cli,pivotal-golang/s3cli,pivotal-golang/s3cli