RFR: 8315774: Enable parallelism in vmTestbase/gc/g1/unloading tests

[Aleksey Shipilev]

Current `vmTestbase/gc/g1/unloading` tests contain 112 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 lightly-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.


$ time CONF=linux-aarch64-server-fastdebug make test TEST="vmTestbase/gc/g1/unloading"

# Current config
 4340.46s user 107.99s system 128% cpu 57:37.79 total

# After this patch
 4138.37s user 84.50s system 808% cpu 8:42.62 total 


Additional testing:
 - [x] 50x Linux AArch64 fastdebug `vmTestbase/gc/g1/unloading`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/15598/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15598&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315774
  Stats: 2576 lines in 112 files changed: 0 ins; 2576 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15598.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15598/head:pull/15598

PR: https://git.openjdk.org/jdk/pull/15598