Tools: Constrain the cryptography package for avoiding breaking changes

The cryptography 35 release causes breaking changes. Some of
certificates are rendered invalid and the package cannot be build
without rust. See
https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst#3500---2021-09-29
for more details.

requirements.txt

@@ -8,7 +8,7 @@ setuptools>=21
 click>=7.0
 pyserial>=3.0
 future>=0.15.2
-cryptography>=2.1.4
+cryptography>=2.1.4,<35
 pyparsing>=2.0.3,<2.4.0
 pyelftools>=0.22