The gathered runtime is for failures/not failures

As long as a future was executed (whether or not
it raised an exception or returned without exception)
the runtime timing sum tracks this time so we should
mention that is what it does/contains.

Change-Id: I52438378c620c0cd4875995c5a3a116b271dc029

taskflow/types/futures.py

@@ -362,7 +362,7 @@ class ExecutorStatistics(object):
 
     @property
     def runtime(self):
-        """Total runtime of all submissions executed."""
+        """Total runtime of all submissions executed (failed or not)."""
         return self._runtime
 
     @property