[jdk11u-dev] RFR: 8272318: Improve performance of HeapDumpAllTest

[Aleksey Shipilev]

Clean backport to improve testing.

Additional testing:
 - [x] Affected test still passes

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

Commit messages:
 - Backport 73da66ffb707abf6dc38368a12e337d52597de25

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/337/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=337&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272318
  Stats: 12 lines in 1 file changed: 12 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/337.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/337/head:pull/337

PR: https://git.openjdk.java.net/jdk11u-dev/pull/337