Finish the work on messages in base runners

[richtja]

In #4662 the helper methods for sending messages was introduced. Unfortunately, they couldn't be used inside runners from avocado/core/nrunner.py because of the problem with distribution of runners with dependencies #4336. When the #4336 will be solved, we should finish the work on #4662 and use messaging methods in avocado/core/nrunner.py