IVGCVSW-7288 ExecuteNetwork fix for multiple outputs

* When a model with multiple outputs was used and output to file, e.g.
with "-w ./boxes,./classes,./scores,./detection", the results where
not saved in the correct files.
* Applies only to the ArmNNExecutor.

Change-Id: I2899322622a4c3fd1d0ddc75b100b81669417660
diff --git a/tests/ExecuteNetwork/ArmNNExecutor.cpp b/tests/ExecuteNetwork/ArmNNExecutor.cpp
index aa71c40..4d63b48 100644
--- a/tests/ExecuteNetwork/ArmNNExecutor.cpp
+++ b/tests/ExecuteNetwork/ArmNNExecutor.cpp
@@ -674,6 +674,7 @@
             }
         }
         std::cout << "\n";
+        ++outputIndex;
     }
 }