AuTest: Switch from curl for proxy_protocol.test.py

[bneradt]

The current proxy_protocol.test.py uses curl to verify Proxy Protocol usage. The gold file for the test expects curl to output the Proxy Protocol header it sends. Recent versions of curl do not output this string anymore. Maybe that's not a big deal - we can probably assume it does send the Proxy Protocol header. But it would probably be preferable to use Proxy Verifier for this test.

[ywkaras]

Is this related to #9550 ?

[bneradt]

Is this related to #9550 ?

Interesting. Thanks for providing the link. Switching to Proxy Verifier will address that. Or, at least, be a helpful part of the process of investigating that.