Upgrade cryptography to 3.4.6 (#8730)

* Upgrade cryptography to 3.4.6

* Fix comment with instructions for how to use hashin

* run tools/rebuild_certbot_constraints.py

* add deps for building cryptography in snaps

* Update cryptography build dependencies for docker

* Update sources for test farm tests

* Remove rust if it's installed for test farm tests

* source bootstrap script and call sudo as needed

tools/docker/core/Dockerfile

@@ -37,6 +37,8 @@ RUN apk add --no-cache --virtual .build-deps \
         openssl-dev \
         musl-dev \
         libffi-dev \
+        python3-dev \
+        cargo \
     && python tools/pipstrap.py \
     && python tools/pip_install.py --no-cache-dir \
             --editable src/acme \