SNOW-27289: HTTP 504 is not retired for PY2

Author: smtakeda

compat.py

@@ -44,7 +44,7 @@
 
     BAD_REQUEST = httplib.BAD_REQUEST
     SERVICE_UNAVAILABLE = httplib.SERVICE_UNAVAILABLE
-    GATEWAY_TIMEOUT = httplib.SERVICE_UNAVAILABLE
+    GATEWAY_TIMEOUT = httplib.GATEWAY_TIMEOUT
     FORBIDDEN = httplib.FORBIDDEN
     UNAUTHORIZED = httplib.UNAUTHORIZED
     INTERNAL_SERVER_ERROR = httplib.INTERNAL_SERVER_ERROR