Runner: add log to know the cancelled reason.

lisa/runner.py

@@ -220,8 +220,8 @@ class RootRunner(Action):
 
             self._start_loop()
         except Exception as identifier:
+            self._log.info(f"canceling runner due to exception: {identifier}")
             cancel()
-            raise identifier
         finally:
             self._cleanup()
 

lisa/util/parallel.py

@@ -102,6 +102,7 @@ class TaskManager(Generic[T_RESULT]):
         self._futures.append(future)
 
     def cancel(self) -> None:
+        self._log.info("Called to cancel all tasks.")
         self._cancelled = True
 
     def check_cancelled(self) -> None: