support/testing/tests/package/test_python_paho_mqtt: new runtime test

This tests valdates that we can publish a message and read it back.

Signed-off-by: Marcus Hoffmann <marcus.hoffmann@othermo.de>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[yann.morin.1998@free.fr:
  - don't manually start mosquitto, there's a startup script for that
  - don't pass custom timeout
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>