connection_dict generated by client can be different in details from the
server side, so pass it thorugh a way how it is treat on the server.

Also, as we are going to be compatible with py3, calculate hash from
sorted items of a dict, instead of relying on side effect of py2 "ordered dict"

https://portingguide.readthedocs.io/en/latest/dicts.html#changed-key-order

Test are focused on client side, and the tricky cases are covered, they
somehow contain the protocol of client <--> server comparision.