Description
Due to OAK-6639, ObservationQueueFullWarnTest.testQueueFullThenFlushing now has a hard-coded sleep to let the test pass on systems which are unable to process init message on observation soon enough.
As proposed there, we should avoid hard-coded sleep and simply wait for our-own-init message for some time - faster system would get it faster, slower systems can wait for it a bit more.