RFR: Loom: [TESTBUG] HumongousStack.java fails with "-XX:-UseCompressedOops"

[Hao Sun]

When running with `-XX:-UseCompressedOops`, much more heap memory would
be consumed, leading to `java.lang.OutOfMemoryError: Java heap space`
error.

In this patch, we increase the maximum heap size to 2GB.

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

Commit messages:
 - Loom: [TESTBUG] HumongousStack.java fails with "-XX:-UseCompressedOops"

Changes: https://git.openjdk.java.net/loom/pull/90/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=90&range=00
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/loom/pull/90.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/90/head:pull/90

PR: https://git.openjdk.java.net/loom/pull/90