Investigate 3.5 test failure

[cicdw]

In #1228 I noticed there was a test that randomly and somewhat mysteriously fails in Python 3.5. It's possibly due to the way mocking / mock state is implemented in 3.5, but I'd like to dig in a little and fully understand it. The relevant test is:

tests/engine/cloud/test_cloud_flows.py::test_deep_map_with_a_retry

[lauralorenz]

We don't support 3.5 anymore, so closing.