Fix/resolve flaky error in tests

[andsel]

Release notes

[rn:skip]

What does this PR do?

Fixes some flaky test acting on 3 things:

• drop from custom low level client the callback mechanism and the queue, but resort just in the queued messages an wait blocking on it.
• updates the Publish collect based on Paho client to release the latch only after having copied the data, to avoid nulls due to read ordering
  From

latch.countDown();
receivedTopic = topic;
receivedMessage = message;

to

receivedTopic = topic;
receivedMessage = message;
latch.countDown();

• in HiveMQ client usages, register the listener to subscribe before the verification and not during the verification. This makes the code less linear, but it's the intended use of the API.

[andsel]

Switch the order so that the latch release happens only after the data has been copied, else the client can read null values.