RFR: 8215097: Do not create NonJavaThreads before BarrierSet

[Kim Barrett]

> On Dec 9, 2018, at 5:37 PM, Roman Kennke <rkennke at redhat.com> wrote:
> Shenandoah also creates workers in constructors. May I request to hold
> this off a little bit to avoid making a mess out of the very soon
> upstream push? I'm open to moving this into initialize() but I cannot
> tell real quick if it has or hasn't any funny side-effects.

Looks like Shenandoah has been pushed.