[tests/system] Update the system tests to the new python-sdk

Summary:
This basically just converts the old system tests to use the new python-sdk.
There's enough code different that it may not make sense to look too much at
the changes but instead just look at the new code.

Test Plan: review the code

Reviewers: kav-ya

Subscribers: khamidou

Differential Revision: https://review.inboxapp.com/D419