[#60058920] Refactor to expose all vegeta stats

Return the entire results hash rather than just pulling the `latencies`
tree. This will allow us to compare other values.

Stuffing the results into a new `res` hash because Long Variable Names.
[#60058920] Check quantity/codes of Vegeta results

Expect that we get the same quantity of requests against the Router and
backend during our timeboxed test, and that all of the responses have 200
status codes.