RFR (XS): Non-updateref closures should not update refs

[Aleksey Shipilev]

Hi,

This is a (performance) regression caused by recent oop iterators consolidation.
Non-updateref closures should do RESOLVE (just read through read barrier),
instead of CONCURRENT (update references):
  http://cr.openjdk.java.net/~shade/shenandoah/markref-resolve/webrev.01/

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey