[AIRFLOW-6625] Explicitly log using utf-8 encoding (apache#7247) (apa…

…che#31)

This is the standard encoding supported by Airflow. We should be explicit about logging using
this encoding.

airflow/utils/log/file_task_handler.py

@@ -52,7 +52,7 @@ def set_context(self, ti):
         :param ti: task instance object
         """
         local_loc = self._init_file(ti)
-        self.handler = logging.FileHandler(local_loc)
+        self.handler = logging.FileHandler(local_loc, encoding='utf-8')
         self.handler.setFormatter(self.formatter)
         self.handler.setLevel(self.level)