test_grpc.py test is broken

[gbregman]

The last change to test_grpc.py caused to stop testing what it was supposed to test. We want to execute CLI commands while update() is running and this is no longer the case. We need to move the sleep to its original position, after the loop of "subsystem list". To take care of the rare case we managed to execute a subsystem list before update had the chance to create a single subsystem we should wait until we see the first subsystem was created and only then go into the loop.