performance-metrics: Successful output should be on stdout not stderr

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

performance-metrics/src/main.rs

@@ -493,7 +493,7 @@ fn main() {
                     .unwrap(),
             )
         } else {
-            Box::new(std::io::stderr())
+            Box::new(std::io::stdout())
         };
 
     report_file