Feature: one-to-one testing mode

[omeh-a]

ipbench is expected to be used with a set of distributed testers, which is exactly what makes it stand out. However, setting this up requires a vast amount of effort and resources. This would effectively gate all outsiders from actually using it.

Goal: a simple way to call a "one-to-one" test from the ipbench controller. This is already possible by running ipbenchd on the same system. As a result, this just means we need to add a way to invoke that in an easy-to-use fashion.

This would allow users to test out ipbench before committing time to set up a cluster of testers (without confusion). As with #10 this is intended to encourage new users to actually give ipbench a try - currently it faces a huge problem in that it is massively functional and genuinely outcompetes alternatives in technical performance, but is all but impossible to pick up without help.