Probe modul ready signal

[djchhp]

Issue

The probe module does not wait for everest to signal ready.

Details

The probe module used for testing is supposed to wait for everest to signal ready. The pattern is to call:

await proble_module.wait_to_ready()

The pattern seems to work, but results in a warning after the tests:
probe_module.py:119: RuntimeWarning: coroutine 'Event.wait' was never awaited

Analysis

There is a problem on two levels.

1. The current implementation does not wait for the ready event, but moves the blocking operation to another thread to be non blocking.
2. Thread safety. Not moving to another thread results in wait_for always waiting until timeout. The reason for this is, that asyncio.Event is not thread safe (https://docs.python.org/3/library/asyncio-sync.html). Since _ready_event.set is called from a different thread than ready_event.wait, wait waits until timeout, since it only learns about being signaled after the timeout.

Proposed solution

Replace asyncio.Event with threading.Event and mimic asyncio.Event behavior by wrapping its wait in a Coroutine.