Problematic backport to 8u: "Ensure tasks use correct number of workers"

[Aleksey Shipilev]

On 10/02/2017 07:50 PM, Zhengyu Gu wrote:
> Simply introduce ShenandoahWorkGang to bypass assertion in FlexibleWorkGang (and avoid contaminate
> upstream).
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/assert_workers_8u/webrev.00/

Thank you, I shall fold it into outstanding jdk8 backports RFR.

For my own checks:

*) Webrev misses the test, do:
 $ hg add test/gc/shenandoah/TestGCThreadGroups.java

*) Excess whitespace after "bool":

  58                    bool  are_ConcurrentGC_threads) :

Otherwise seems fine.

Thanks,
-Aleksey