RFR[8u backport] 8213992: Rename and make DieOnSafepointTimeout the diagnostic option

[Zhengyu Gu]

Hi,

I would like to backport this RFE, it helps to debug long safepoint sync 
time.

Bug: https://bugs.openjdk.java.net/browse/JDK-8213992
Original review: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2018-November/035255.html

Backport has only minor conflicts.
Backport Webrev: http://cr.openjdk.java.net/~zgu/8213992-8u/webrev.00/


Thanks,

-Zhengyu