RFR 8233850: Shenandoah: Shenandoah thread count ergonomics should be container aware

[Roman Kennke]

Looks good to me. Thanks!

Roman


> Please review this small patch that uses container-aware
> os::initial_active_processor_count() API for calculating worker thread
> count ergonomics.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8233850
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8233850/webrev.00/
> 
> Test:
>   hotspot_gc_shenandoah (fastdebug and release)
> 
> 
> Thanks,
> 
> -Zhengyu
>