example code bug in remote_server_context.py

[MarekLew]

In file:
https://github.com/riptideio/pymodbus/blob/master/examples/contrib/remote_server_context.py#L160

RemoteServerContext not have self.__slaves

more in:
fec7ac3

[dhoomakethu]

There you go, #4736b0f , Thats just an example and not a part of main library. Please feel free to do the changes and raise PR. The changes for __iter__ is done inline with python 3 compatibility. I am closing this issue. Please comment on the PR, if you have further concerns.