Fix/3.x/bt 3963 aws v4 signer

This replace the AWS v2 signer by a version that does v4 signing. I've removed the old V2 signer : There is no reason to keep it in, since all regions support V4, and for some regions (eu-central-1, China) it is mandatory.

Yes, the're official testing credentials provided by AWS. The're also used in al there examples.