AbstractTransportTest.openStreamPreventsTermination is flaky on Windows

Seen in https://grpc-testing.appspot.com/job/gRPC-Java-PR-Windows/2337/console

```
io.grpc.netty.NettyTransportTest > openStreamPreventsTermination FAILED
java.io.IOException: Failed to bind

Caused by:
java.net.BindException: Address already in use: bind

java.lang.AssertionError

187 tests completed, 1 failed, 3 skipped
:grpc-netty:test FAILED
```

Start with AbstractTransportTest.openStreamPreventsTermination and the grpc-netty test failure shown in the Windows build log. Reproduce the test on Windows and inspect the bind failure. Done means the test completes reliably without Address already in use failures on Windows.

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