RFR: 8316142: Enable parallelism in vmTestbase/nsk/monitoring/stress/lowmem tests

[Aleksey Shipilev]

Similar to [JDK-8315437](https://bugs.openjdk.org/browse/JDK-8315437), current vmTestbase/nsk/monitoring/stress/lowmem tests contains 36 tests, each running exclusively. This drags the tier4 test times up. There seem to be no reason to run these tests exclusively, though: they complete in reasonable time, are moderately-threaded, and consume the usual amount of memory.

We should consider enabling parallelism for them and get improved test performance. Currently it is blocked by TEST.properties with exclusiveAccess.dirs directives in them.

Current run on 18-core machine:
 6385.39s user 8568.61s system 1308% cpu 19:02.97 total

Fully parallel:
 3885.67s user 295.13s system 2772% cpu 2:30.77 total 

Additional testing:
 - [x] 100x Linux x86_64 fastdebug, `vmTestbase/nsk/monitoring/stress/lowmem`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/15689/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15689&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316142
  Stats: 828 lines in 36 files changed: 0 ins; 828 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15689.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15689/head:pull/15689

PR: https://git.openjdk.org/jdk/pull/15689