R1:fde02c4b4edf

Fix protocol serve detection for clustered repositories that terminate HTTPS

Summary:
Ref T10927. Pretty sure the issue is:

- User makes an HTTPS request.
- Load balancer terminates it, but with an `X-Forwarded-Proto` header.
- `secure001` (or whatever; acting as web host) proxies it to `secure002` (or whatever; acting as a repository host). **This** connection is plain HTTP.
- Since this proxied connection is plain HTTP, we check if the repository can serve over "http", but it can't: only…