RFR [sh/8u]: Do not enable UseCountedLoopSafepoints in Shenandoah by default

[Roman Kennke]

>> http://cr.openjdk.java.net/~rkennke/clsp/webrev.01/
> 
> Yes.
> 
> I would add this comment:
> 
>    // Shenandoah cares more about pause times, rather than raw throughput.
>    // Enabling safepoints in counted loops makes it more responsive with
>    // long loops. However, it is risky in 8u, due to bugs it brings, for
>    // example JDK-8176506. Warn user about this, and proceed.
>    if (UseCountedLoopSafepoints) {
> 
> Looks good otherwise.

Ok, good. I added the comment and pushed the change.

Thanks,
Roman