We've historically been pretty flexible with the version of

cryptography installed, leaving more explicit version ranges up to

other dependencies. However, a situation was found where older versions

of pyOpenSSL outright break the system (impacting pip) when

newer versions of cryptography are installed, and that can break

Review Board, leading to an install nightmare.
This is documented here: https://github.com/pyca/pyopenssl/issues/1143
While we don't use pyOpenSSL ourselves, we want to ease installation.

The easiest way to do this is to ensure we're depending on both a modern

cryptograph (which will also help us avoid Python version breakages

down the road), and a compatible pyOpenSSL.
pyOpenSSL is a pure-Python package, and doesn't add any new

dependencies we don't already explicitly or implicitly depend on, so

it should be fairly safe.

Installed the dependencies on all supported versions of Python.
Verified that pyOpenSSL didn't result in any additional packages

installed.