[Python] Operation rename and bug fix

[annatisch]

Fix for issues #1196 and #1165

[tbombach]

👍 LGTM

[annatisch]

@lmazuel - I've made a couple of minor changes to serialization.py, if you could do a quick review :)
They should not be breaking, and I doubt are used by the existing clients so may not need a new release yet.

Effectively it's a change to support default/constant date and datetime values by allowing strings to passed in instead of date or datetime objects. The strings would need to already be in the correct ISO formatting that the request will serialize to. Let me know if you think this is okay.

[annatisch]

@tbombach, @lmazuel,

Sorrry guys - I have to rebase the PR in order to merge and a bunch of other bug fixes got added to the PR - could I trouble you to take another look at the latest changes?
Fixes included for #1196, #1165 and #1304.

This PR also includes a fix to Python SDK bug #697

Please don't merge until @lmazuel has signed off that the Python SDK bug has been fully address to his liking.

Thanks!!

[tbombach]

Looks good to me! I'll hold off on merging until Laurent signs off

[lmazuel]

@tbombach I take a look right now and tell you asap.
However, it's important to merge #1338 first when the tests here will be ok (a critical bug I had to fix in emergency).
Thanks!

[lmazuel]

@tbombach All Python SDK for services are green. I valid this!

[tbombach]

Merged