avocado: limit parallel tasks to 1 with nrunner

[ana]

With version 91.0 Avocado have switched the default runner from an implementation named internally runner to a new architecture, that allows parallel execution of tests, called nrunner. Please, find more info at https://avocado-framework.readthedocs.io/en/91.0/releases/91_0.html and https://avocado-framework.readthedocs.io/en/91.0/guides/contributor/chapters/runners.html?highlight=nrunner-max-parallel-tasks

In the case of pok, you could continue using the legacy runner, setting --test-runner=runner and sticking to the next LTS version that will be 92.0 or switch to nrunner and disable parallel execution by setting --nrunner-max-parallel-tasks 1

Signed-off-by: Ana Guerrero Lopez [email protected]