Create latency test

[gavv]

Similar to #1, which will measure "service quality" (in other words, number of losses/drops), we want to add an automated test that will measure latency.

I have a project that implements latency measurement: https://github.com/gavv/signal-estimator

It is tool, not a library, but it has an issue for implementing a library with C API: gavv/signal-estimator#33

We can implement that issue, and then implement a test in rt-tests, which will:

• ask signal-estimator library to produce output frames
• pass these frames to roc sender
• in another thread, retrieve frames from roc receiver
• pass retrieved frames to signal-estimator
• ask signal-estimator for measured latency and report it