RFR: 8258383: vmTestbase/gc/g1/unloading/tests/unloading_compilation_level[1, 2, 3] time out without TieredCompilation

[Tobias Hartmann]

The test gets stuck while waiting for a compilation to succeed, because the corresponding compilation level is not available since Tiered Compilation is disabled (or `TieredStopAtLevel` is set). The tests should not be executed without Tiered Compilation (or if the requested compilation level is not available) and also check the output of `enqueueMethodForCompilation` for sanity.

Thanks,
Tobias

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Commit messages:
 - 8258383: vmTestbase/gc/g1/unloading/tests/unloading_compilation_level[1,2,3] time out without TieredCompilation

Changes: https://git.openjdk.java.net/jdk/pull/2125/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2125&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258383
  Stats: 75 lines in 25 files changed: 50 ins; 0 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2125.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2125/head:pull/2125

PR: https://git.openjdk.java.net/jdk/pull/2125