RFR: 8023113: tools/jar/ChangeDir.java fails if /tmp/a exists

[Xueming Shen]

Hi,

Please help the small update to the test case tools/jar/ChangeDir.java,
which might fail if the "dedicated" test directory /tmp/a exists and the
user does not have privilege to delete/clean it up.

The proposed change here is to use a random file name (from File.getTempFile())
for the top test directory (instead of the fixed /tmp/a), and really clean it up
after testing (the old test leaves /tmp/a and those temp files undeleted).

http://cr.openjdk.java.net/~sherman/8023113/webrev

Thanks,
-Sherman