RFR: 8366692: Several gc/shenandoah tests timed out

[SendaoYan]

Hi all,

After JDK-8260555 set the default jtreg timeout factor to 1, then several gc/shenandoah tests run timed out with jtreg options -timeoutFactor:1. So I think it's necessary to increase the timeout value set in tests to make test run normally.

The actual run time consumed on my linux-x64 machine with  224 CPU core threads shows in [JDK-8366692](https://bugs.openjdk.org/browse/JDK-8366692).

Accodring the time statistics, the test test/hotspot/jtreg/gc/shenandoah/TestSieveObjects.java only change the second `@run` at the `@test id=generational` and `@test id=aggressive`, other tests do not need to change. And all the `@run` in test test/hotspot/jtreg/gc/shenandoah/jni/TestJNIGlobalRefs.java changed from 120(default value) to 240.

Change has been verified locally on linux-x64, test-fix only, no risk.

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Commit messages:
 - add timeout value for @aggressive
 - 8366692: Several gc/shenandoah tests timed out

Changes: https://git.openjdk.org/jdk/pull/27052/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27052&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366692
  Stats: 6 lines in 2 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27052.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27052/head:pull/27052

PR: https://git.openjdk.org/jdk/pull/27052