JDK 9 RFR of 8175115: Improve instrumentation of java/nio/file/WatchService/LotsOfEvents.java

[Brian Burkhalter]

Please review this test-only change at your convenience.

Issue:	https://bugs.openjdk.java.net/browse/JDK-8175115
Patch:	http://cr.openjdk.java.net/~bpb/8175115/webrev.00/

In case of detecting an insufficient number of file creation or deletion events, attempt one more long polling of the WatchService to see whether more events might be detected given a longer timeout, and print extra information about the number of events detected versus expected, and the number of existing files.

Thanks,

Brian