Currently we try to use `https://` when we see `https_host`, however
that doesn't work and results in errors like `Received error: fetch
control key: Get "https://controlplane.tailscale.com/key?v=32":
proxyconnect tcp: tls: first record does not look like a TLS handshake`
This indiciates that we are trying to do a HTTPS request to a HTTP
server. Googling suggests that the standard is to use `http` regardless
of `https` or `http` proxy
Updates #4395, #2605
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Maisem Ali