Places the CommonResponse struct at the *end* of all IAM responses. (#8537)

* Places the CommonResponse struct at the end of all IAM responses, rather than the start.

* iam: fix error response request id layout

* iam: add XML ordering regression test

* iam: share request id generation

---------

Co-authored-by: Aaron Segal <aaron.segal@rpsolutions.com>
Co-authored-by: Chris Lu <chris.lu@gmail.com>

weed/s3api/s3api_embedded_iam.go

@@ -162,6 +162,7 @@ func newIamErrorResponse(errCode string, errMsg string) iamErrorResponse {
 	errorResp.Error.Type = "Sender"
 	errorResp.Error.Code = &errCode
 	errorResp.Error.Message = &errMsg
+	errorResp.SetRequestId()
 	return errorResp
 }