test: make the forwarding test more realistic using HTTP
test: make the forwarding test more realistic using HTTP

This also makes it easier to extend in future, for example to make
a simple interop test with `curl`.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit