1.3.11: Remove cryptography > 3 support

- Added the incompatiblity of cryptography to the dockerfile.
- 1.3.10 broke dependencies because the docker didn't pull
the project constraints.
- Added a constraints specific for python2 users, other can continue
using the python3 one.

This should allow:
 - Making sure further version's docker stay compatible
 - easier maintenance of python2 vs python3 compatibility.

This does not fix forward compatiblity with cryptography,
but at least make the current build work.