Add cryptography installation (#7404)

To avoid ModuleNotFoundError due to no module named 'setuptools_rust',
this adds cryptography installation to requirements.txt.

Created by jfc-evs originally as https://github.com/kubernetes-sigs/kubespray/pull/7264

requirements.txt

 ansible==2.9.18
+cryptography==2.8
 jinja2==2.11.3
 netaddr==0.7.19
 pbr==5.4.4