RFR: After Evac verification should run consistently

[Aleksey Shipilev]

Looking at GC logs, realized that "After Evac" verification is not always running, where needed. The
reason for that is, UR is optional and we have an incorrect shortcut in the block that decides to do
this verification. Moving the code close to the actual decision about UR makes it correct and cleaner:
  http://cr.openjdk.java.net/~shade/shenandoah/verifier-after-evac/webrev.01/

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey