8028589: Instrument tools/jar/JarEntryTime.java to make it easier to diagnose failures

[Alan Bateman]

The test tools/jar/JarEntryTime.java has been failing intermittently 
(but very rarely) for some time. The failure seems to be that the 
extracted time it out by more than 10 seconds compared to the original 
file time but it isn't always so (esp. when the test runs in a fraction 
of a second). I'd like to add instrumentation to the test so that if it 
fails again (and someone is good enough to report it) then we  at least 
have the timestamps in the logs. The webrev with the proposed change is 
here:
   http://cr.openjdk.java.net/~alanb/8028589/webrev/

Thanks,
Alan.