[AIRFLOW-1917] Trim extra newline and trailing whitespace from log (apache#3862)

Author: ckljohn

airflow/utils/log/logging_mixin.py

@@ -92,7 +92,7 @@ def write(self, message):
             self._buffer += message
         else:
             self._buffer += message
-            self.logger.log(self.level, self._buffer)
+            self.logger.log(self.level, self._buffer.rstrip())
             self._buffer = str()
 
     def flush(self):

tests/utils/test_logging_mixin.py

@@ -86,8 +86,8 @@ def test_write(self):
 
         self.assertEqual(log._buffer, msg)
 
-        log.write("\n")
-        logger.log.assert_called_once_with(1, msg + "\n")
+        log.write(" \n")
+        logger.log.assert_called_once_with(1, msg)
 
         self.assertEqual(log._buffer, "")