Fix the Nginx configuration during integration tests (#6801)

If you execute `tests/lock_test.py` or `tox -e integration` on a fairly recent machine, you will get the following error during tests executing against a live Nginx instance:
```
no "ssl_certificate" is defined in server listening on SSL port while SSL handshaking, client: x.x.x.x, server: y:y:y:y:z
```

Indeed, having no defined ssl certificate for a ssl port would inevitably lead to an error during the handshake SSL process between a client and this mis-configured nginx instance.

However it was not a problem one year before, because the handshake was not occurring in practice: the test just need to have a nginx started, and then immediately proceed to modify the configuration with a correct SSL setup. And nginx was able to start with a mis-configuration on SSL. 

But then this fix has been done: https://trac.nginx.org/nginx/ticket/178

Basically with this, validation of the configuration is done during nginx startup, that will refuse to start with invalid configuration on SSL. Consequently, all related tests are failing with a sufficiently up-to-date nginx. For now, it is not seen on Travis because Ubuntu Trusty is used, with an old Nginx.

The PR fixes that, by generating on the fly self-signed certificates in the two impacted tests, and pushing the right parameters in the Nginx configuration.

* Fix nginx configuration with self-signed certificates generated on the fly

* Fix lint/mypy

* Fix old cryptography

* Unattended openssl

* Update lock_test.py

certbot-nginx/tests/boulder-integration.sh

@@ -7,8 +7,12 @@ export PATH="/usr/sbin:$PATH"  # /usr/sbin/nginx
 nginx_root="$root/nginx"
 mkdir $nginx_root
 
+# Generate self-signed certificate for Nginx
+openssl req -new -newkey rsa:2048 -days 1 -nodes -x509 \
+    -keyout $nginx_root/cert.key -out $nginx_root/cert.pem -subj "/CN=nginx.wtf"
+
 reload_nginx () {
-    original=$(root="$nginx_root" ./certbot-nginx/tests/boulder-integration.conf.sh)
+    original=$(./certbot-nginx/tests/boulder-integration.conf.sh $nginx_root $nginx_root/cert.key $nginx_root/cert.pem)
     nginx_conf="$nginx_root/nginx.conf"
     echo "$original" > $nginx_conf