Most of the gRPC-related unit tests rely on a constant to determine which port to listen to. This can lead to spurious test failures if two tests happen to be running at the same time.

For example, in this failure, you can see in the logged metadata that connections from transport_test (pid 9264) interfered with the "AllowInvalidClientCertificate" test of grpc_transport_layer_test (pid 3140). Likewise, connections from tranport_layer_test interfered with "MarkKillOnGRPCClientDisconnect" test of transport_test.

We should update these tests to rely on ephemeral ports to avoid these kinds of collisions.