Option to set number of parallel tests

[veaceslavdoina]

We have short and long lasting tests.

Short ones may take from minutes to hours and long from hours to days. To speed up tests run we may consider to run them in parallel. And to exclude any interference between the codex nodes from different tests we should Check network policies applied during the tests #12.

Because network policies require a network plugin which require additional configuration to work on Docker Desktop Kubernetes, policies will not work locally even if applied. And for local run we should execute them in sequence instead.

To optimize run inside the remote Kubernetes cluster we should have an option to define number of parallel tests to run via CLI or environment variable.