The default is kept as no retries. Since retries with exponential
backoff are a good thing to make easy, the int form defaults to
setting a backoff_factor.
Unfortunately, urllib3 retry backoff does not implement jitter.
Switching this to use the `backoff` library[1] rather than urllib3's
native Retry is left as future extension.
[1] https://pypi.org/project/backoff/