py-cryptography soon will need rust

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

I wanted to update py-cryptography to the latest version, since it's
security-related software and we should be tracking head. This is not
used by much software in pkgsrc, but notably by py-certbot, a software
for keeping your Let's Encrypt-certificates up-to-date.

py-cryptography's latest version doesn't support python 2.7 any
longer, so I imported the last version that does as
security/py27-cryptography.

While updating, I found out that for building (but not for running!)
the latest py-cryptography, it needs rust.

I understand where py-cryptography's authors are coming from, they
want fast and secure software, and rust is claiming that space.

lang/rust on NetBSD supports aarch64*, armv7, i386, powerpc, sparc64,
x86_64, so it covers quite a number of platforms already. Building
rust itself takes a lot of resources, but we also have lang/rust-bin
using pre-built binaries.

I suggest we update py-cryptography to the latest version (including
the rust build dependency). The candidate package is in
wip/py-cryptography. I think that rust support in pkgsrc is good
enough that we can do this unconditionally.

If you think that is not the case, please let me know, and preferably
also offer suggestions what to do instead.

Cheers,
 Thomas