Fix potential issue around resolving localhost to IPv6 on Windows (patroni#3380)

When specifying `0.0.0.0` or `127.0.0.1` in `listen_addresses`, Postgres won't listen on IPv6 (in other words, these addresses imply IPv4 only).  However, the typical Windows system will have a preference to resolve `localhost` to `::1`.

While one can change these preferences, it's unclear if it has unwanted side effects.  Instead of this, the proposed small change fixes this behavior.

Author: avandras

patroni/postgresql/config.py

@@ -1102,8 +1102,11 @@ def _get_tcp_local_address(self) -> str:
         listen_addresses = self._server_parameters['listen_addresses'].split(',')
 
         for la in listen_addresses:
-            if la.strip().lower() in ('*', '0.0.0.0', '127.0.0.1', 'localhost'):  # we are listening on '*' or localhost
+            if la.strip().lower() in ('*', 'localhost'):  # we are listening on '*' or localhost
                 return 'localhost'  # connection via localhost is preferred
+            if la.strip() in ('0.0.0.0', '127.0.0.1'):  # Postgres listens only on IPv4
+                # localhost, but don't allow Windows to resolve to IPv6
+                return '127.0.0.1' if os.name == 'nt' else 'localhost'
         return listen_addresses[0].strip()  # can't use localhost, take first address from listen_addresses
 
     def resolve_connection_addresses(self) -> None: