RFR: Rehash -XX:-UseTLAB in tests

[Aleksey Shipilev]

We added these while hunting for partial collections bug around TLABs. Which was identified as the
problem with marked, but unreachable objects. Today, Verifier checks marked objects too, obviating
the need for these tests. Rehasing them save ~5 min per testing round, because GCBasher is on the
critical path. Some basic sanity tests are left to check that out-of-TLAB allocation still works.

Webrev:
  http://cr.openjdk.java.net/~shade/shenandoah/tests-tlab/webrev.01/

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey