RFR: 8058550: Clarify that TimerTasks are not reusable

[Martin Buchholz]

Hi Chris,

I'd like you to do a code review.

http://cr.openjdk.java.net/~martin/webrevs/openjdk9/TimerTask-clarification/
https://bugs.openjdk.java.net/browse/JDK-8058550