Limit tests to a single thread
Limit tests to a single thread

The tests spin up local helper applications on fixed ports. Running tests in
parallel breaks them.

advancedtelematic/aktualizr,advancedtelematic/aktualizr,advancedtelematic/aktualizr,advancedtelematic/aktualizr,advancedtelematic/sota_client_cpp,advancedtelematic/sota_client_cpp