RFR: JDK-8302129: Make MetaspaceReclaimPolicy a diagnostic switch [v2]

[Thomas Stuefe]

> See associated CSR for background and motivation: https://bugs.openjdk.org/browse/JDK-8302130 .
> 
> This patch is technically trivial. CSR is approved.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  fix release tests

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12540/files
  - new: https://git.openjdk.org/jdk/pull/12540/files/dbddc6b0..717a3ae9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12540&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12540&range=00-01

  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/12540.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12540/head:pull/12540

PR: https://git.openjdk.org/jdk/pull/12540