Tests: block until grpc server has stopped
This is an attempt to fix #281 (closed). Reproducing that issue is hard. I ran 1 experiment with the tests in a loop where the error occurred after about 15 minutes. I ran 1 other experiment with this branch where the tests ran in a loop for 30 minutes without hitting the panic.
Closes #281 (closed).
Edited by Jacob Vosmaer