This commit adds a new `https_serve_directory()` test helper
and some custom self-signed and worthless certs that are used
during testing. They are not dynamically generated to avoid the
extra compuation time during tests (but they could be).
Generated via:
```
$ openssl req -new -newkey rsa:2048 -nodes -x509 \
-subj "/C=DE/ST=Berlin/L=Berlin/O=Org/CN=localhost" \
-keyout "key1.pem" -out "cert1.pem"
```
This will allow us to test `https` download URLs as well in e.g.
the curl source.
When using a modern curl we can download download multiple urls
in parallel which avoids connection setup overhead and is generally
more efficient. Use when it's detected.
TODO: ensure both old and new curl are tested automatically via
the testsuite.
Only py3.7+ has ThreadingHTTPServer and SimpleHTTPRequestHandler
that can take a directory argument. We could reimplement this
on py36 (easy for threading, harder for missing directory) but
instead this commit just skips tests that try to use a
ThreadingHTTPServer.
Remove once we no longer support py3.6.
To test the curl sources it is very useful to have a small httpd
server that can serve an arbitrary directory. This helper will
ensure that via:
```python
with with osbuild.testutil.net.http_serve_directory(fake_httpd_root) as httpd:
port = httpd.server_port
# download from http://localhost:{port}/<any-path-under-httpd-root>
```
