[8u] 8178870: instrumentation.retransformClasses cause coredump

[Zhengyu Gu]

I would like to backport this patch to 8u, as it is on Oracle 8u 
backport list.

The original patch does not apply cleanly.

1) Missing get_ik() function in jvmtiRedefineClasses.cpp in 8u code 
base. I imported get_ik() into 8u code base.
2) _scratch_classes was declared as Klass** in 8u, but InstanceKlass** 
in 10. Added casting in 8u code.
3) Missing test infrastructure in 8u, converted test to shell script.

Original bug: https://bugs.openjdk.java.net/browse/JDK-8178870
Original code review: 
https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-October/024727.html


8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8178870-8u/webrev.00/

Thanks,

-Zhengyu