Signature check fails in case of non default service path

[varpa89]

I'd like to handle s3proxy queries on non root query path, so I set it to /s3 via servicePath property in S3ProxyHandler constructor.
When we use AWS_V2_OR_V4 authenticationType a query fails with SIGNATURE_DOES_NOT_MATCH error.

I investigated a bit and found possible reason: uriForSigning is built from this.servicePath + originalUri, so the servicePath value is duplicated in the final string.
But on the first branch of if/else condition different variables used - this.servicePath + uri