Better cleanup for jdk/test/java/io/File/createTempFile/NameTooLong.java

NameTooLong.java creates files in the default temp directory, but does not clean up later.

cat -n jdk/test/java/io/File/createTempFile/NameTooLong.java
 [...]
    46 f = File.createTempFile(ps[0], ps[1]);

The preferred approach would be to create temporary test files under the jtreg property user.dir instead.

During a jtreg run, user.dir has the value $PWD/JTwork/scratch