RFR: Fix parallel object-monitor scanning

[Aleksey Shipilev]

On 11/24/2016 02:57 PM, Roman Kennke wrote:
> I observed an assert being thrown in the parallel object-monitor
> scanner, and it happens because we don't always scan the object-monitor 
> roots. The ShenandoahRootProcessor for initial-evacuation will not use
> it, and therefore not find any CLAIMED blocks.

> http://cr.openjdk.java.net/~rkennke/fixparsync/webrev.00/

Looks okay as the stop-gap measure.

Although the lifecycle for ParallelObjectSynchronizerIterator is odd,
and we should not probably do the recovery in destructor, to start with:
only do the after-iteration fixups when the actual iteration happened?
Let's leave that part to Zhenguy :)

Thanks,
-Aleksey