8203765: java/nio/channels/Selector/SelectAndClose: add some prints and @intermittent tag

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8203765
http://cr.openjdk.java.net/~bpb/8203765/webrev.00/

This test-only change modifies the information printed on failure and adds the @intermittent tag as the test fails occasionally albeit rarely.

Thanks,

Brian