Add validation to test harness that every endpoint is being tested

[njgheorghita]

In one way or another, we want the test harness run to fail if it hasn't run against every currently implemented TrinEndpoint

re: #148 (comment)

[njgheorghita]

Closing since this is really hard to do ince all of the endpoints are stored as a large enum, which you cannot iterate through easily in rust. Further complications come from the fact that we might want one test for some endpoints and multiple for others. General guideline is that as you add a jsonrpc endpoint, you should also add tests to peertest