RFR: 8268699: Shenandoah: Add test for JDK-8268127

[Zhengyu Gu]

Large pages on x86 is 2m and Shenandoah expects >= 10 minimal regions, so heap size has to be < 20m to verify JDK-8268127.

Test:

- [x] Passed new test on Linux x86_64

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

Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/4486/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4486&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268699
  Stats: 71 lines in 1 file changed: 71 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4486.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4486/head:pull/4486

PR: https://git.openjdk.java.net/jdk/pull/4486