Add the error code to the worker error logged to redis

buildman/jobutil/workererror.py

@@ -94,7 +94,10 @@ class WorkerError(object):
   def extra_data(self):
     if self._base_message:
       return {
-          'base_error': self._base_message
+          'base_error': self._base_message,
+          'error_code': self._error_code
       }
 
-    return {}
+    return {
+        'error_code': self._error_code
+    }