[EWT-499] Airflow Upgrade to 1.10.12 [CP] from 1.10.4+twtr : 7b52a71

*Cherry-Pick contains [CP][AIRFLOW-3121] Define closed property on StreamLogWriter (apache#3955) (twitter-forks#52)

CP of 2d5b8a5

airflow/utils/log/logging_mixin.py

@@ -80,6 +80,7 @@ def _set_context(self, context):
             set_context(self.log, context)
 
 
+# TODO: Formally inherit from io.IOBase
 class StreamLogWriter(object):
     """
     Allows to redirect stdout and stderr to logger