JDK 9 RFR of 8176744: Improve internal timing of java/nio/channels/Selector/SelectAndClose.java

[Brian Burkhalter]

Please review this test-only fix at your convenience.

Issue:	https://bugs.openjdk.java.net/browse/JDK-8176744
Patch:	http://cr.openjdk.java.net/~bpb/8176744/webrev.00/

Deal with another flaky use of sleep().

Thanks,

Brian