The following error occured on Windows when switching to using HTTPS
url with Twisted Agent:
```
<class 'twisted.web._newclient.ResponseNeverReceived'>: [<twisted.python.failure.Failure OpenSSL.SSL.Error: [('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')]>
```
The fix is to install certifi and provide the path to the trust store as
env var for OpenSSL to pick up.
Also includes a simplication of the core test_listen_port code.
It can be useful to have the build folder available so zip it up for
download as an artifact.
Although the 7z has an exclude for the installer exe it doesn't seem to
be working.