JDK 9 RFR of 8160220: (fs) Tests in jdk/test/java/nio/file/WatchService leave directory trees behind

[Brian Burkhalter]

Please review at your convenience.

Issue:	https://bugs.openjdk.java.net/browse/JDK-8160220
Patch:	http://cr.openjdk.java.net/~bpb/8160220/webrev.00/

Summary:

1) DeleteInterference & LotsOfCancels

Create temporary files in a directory specifiable via the “test.dir” property with default “.”.

2) LotsOfCancels

Add (probably redundant) deletion of temporary file tree.

Thanks,

Brian