In this test, we
1. make a streaming RPC on a connection
1. graceful stop it to send a GOAWAY
1. hard stop it, so the client will create a connection to another server
Before this fix, 2 and 3 can happen too soon, so the RPC in 1 would fail
and then transparent retry (because the stream is unprocessed by the
server in that case).
This retry attempt could pick the new connection, and then the RPC would
block until timeout.
After this streaming RPC fails, we make unary RPCs with the same
deadline (note: deadline not timeout) as the streaming RPC and expect
them to succeed. But they will also fail due to timeout.
The fix is to make a round-trip on the streaming RPC first, to make sure
it actually goes on the first connection.