Support AWS signature version 4 in object storage benchmarks

The command `aws s3 rm s3://pkb7b019bc1 --recursive` on a bucket in the region `eu-central-1` results in the error

> "You are attempting to operate on a bucket in a region that requires Signature Version 4. You can fix this issue by explicitly providing the correct region location using the --region argument, the AWS_DEFAULT_REGION environment variable, or the region variable in the AWS CLI configuration file. You can get the bucket's location by running "aws s3api get-bucket-location --bucket BUCKET""

We should fix this.