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

[Zhengyu Gu]

Hi,

Please approve the backport of JDK-8213992 to 8u, it helps to diagnose 
long safepoint sync time.

Bug: https://bugs.openjdk.java.net/browse/JDK-8213992
JDK12 changeset: http://hg.openjdk.java.net/jdk/jdk/rev/639a3e43f5b7
JDK12 review thread: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2018-November/035255.html

JDK8u webrev: http://cr.openjdk.java.net/~zgu/8213992-8u/webrev.00/
JDK8u review thread: 
http://mail.openjdk.java.net/pipermail/jdk8u-dev/2018-November/008200.html

Thanks,

-Zhengyu