RFR: Update region sampling to include TLAB/GCLAB allocation data

[Aleksey Shipilev]

Hi,

It seems useful to see TLAB/GCLAB allocations in Visualizer. Additionally, this
fixes "recycled" region flag handling that is updated at the inconvenient time,
and when heap region sampling is actually disabled. It does update counters on
allocation path, but that path is only normally taken to claim entire TLABs.

Webrev:
  http://cr.openjdk.java.net/~shade/shenandoah/sampling-gclabs/webrev.01/

Going to commit the same to 8u too.

Testing: hotspot_gc_shenandoah; Visualizer runs with some workloads

Thanks,
-Aleksey