prop224: Deeper testing of HS ntor subsystem
Currently we have integration tests that cross-verify our little-t-or HS ntor implementation with a reference python implementation.
However, those tests don't go deep enough into verifying and parsing the actual INTRODUCE/RENDEZVOUS cell contents like our regular ntor integration tests. Instead they just test that the ntor results are consistent between the C and python implementations.
When we implement the whole cell logic on the client and service side, we should test the HS ntor subsystem deeper.