RFR: Added ZGC executors and test for object alignment detection

[Anton Rybochkin]

This test reveals incorrect object alignment detection when using generational ZGC which results in high object size reported (512k on aarch64 and 64k otherwise)

-------------

Commit messages:
 - Added test executions with ZGC
 - Added test for object alignment detection

Changes: https://git.openjdk.org/jol/pull/64/files
  Webrev: https://webrevs.openjdk.org/?repo=jol&pr=64&range=00
  Stats: 108 lines in 2 files changed: 108 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jol/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/jol.git pull/64/head:pull/64

PR: https://git.openjdk.org/jol/pull/64