8205641: Make java/nio/channels/Selector/RacyDeregister.java noisier and flush after prints

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8205641
http://cr.openjdk.java.net/~bpb/8205641/webrev.00/

Please review this small sub-task patch to make some changes to the test which will hopefully facilitate diagnosing the timeouts observed.

Thanks,

Brian