Use `logger.error` instead of `printStackTrace` in HarryRunner.
diff --git a/harry-runner/src/harry/runner/HarryRunner.java b/harry-runner/src/harry/runner/HarryRunner.java
index a18885b..3adf9c0 100644
--- a/harry-runner/src/harry/runner/HarryRunner.java
+++ b/harry-runner/src/harry/runner/HarryRunner.java
@@ -72,7 +72,7 @@
             }).get(run.snapshot.run_time_unit.toSeconds(run.snapshot.run_time) + 30,
                    TimeUnit.SECONDS);
             if (result instanceof Throwable)
-                ((Throwable) result).printStackTrace();
+                logger.error("Execution failed", result);
 
         }
         catch (Throwable e)