RFR: 8260349: Cannot programmatically retrieve Metaspace max set via JAVA_TOOL_OPTIONS

[David Holmes]

A simple but long standing bug whereby the MemoryPool MXBean only sees the value of MaxMetaspaceSize if it was set directly on the command-line and not by other means (e.g. env var).

Fix is to check !FLAG_IS_DEFAULT rather than FLAG_IS_CMDLINE.

Expanded regression test added (based on the reproducer in the JBS issue) that checks all the ways to set the flag: cmd-line, env-var, hotspotrc file

Testing: regression test (before and after fix)
             tiers 1-3 (in progress)

Thanks,
David

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Commit messages:
 - Reduced test code using loop for env-vars
 - 8260349: Cannot programmatically retrieve Metaspace max set via JAVA_TOOLS_OPTIONS

Changes: https://git.openjdk.java.net/jdk/pull/2275/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2275&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260349
  Stats: 121 lines in 2 files changed: 118 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2275.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2275/head:pull/2275

PR: https://git.openjdk.java.net/jdk/pull/2275