Add exponential backoff timeout to test

[uaalto]

Closes #2968

Adapts the test to reduce the timeout within a lower boundary to keep it reasonable. Without this, the test depend on the system, which will require continuous tuning and/or complicate reproducibility.

[myleshorton]

For some reason I thought the issue with the test was with the cert itself. Does it just appear that way but is actually an issue with the timeout @uaalto?

[uaalto]

The previous error was caused by the connection succeeding and then trying to do the TLS handshake. Because we didn't provide any certificates in the test code (assuming it wasn't going to reach that stage), it was failing to use a proper certificate.
Once this was fixed, it turns out that sometimes the the 5000 microseconds timeout is too high, and the connection actually succeeds. The test relies on the connections timing out. Since I couldn't replicate the issue after 1000 runs in my machine, I assumed that it depends a lot on the machine, so I propose a way to adapt to faster machines.
The code will just reduce the max value of the timeout and repeat the test. It will do this until a connection succeeded in a suspiciously low time, which will be logged for further investigation.

[myleshorton]

Gotcha -- OK let's give it a shot!