[master] RFR: Don't warn when UCOH is on by default

[Stefan Karlsson]

When running testing with UCOH enabled by default in the code and non-generational ZGC the JVM prints this warning, which causes multiple failures in the testing. I'd like to propose that we  (at least temporarily) only write this warning if the user explicitly asked for UCOH.

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Commit messages:
 - Don't warn when UCOH is on by default

Changes: https://git.openjdk.org/lilliput/pull/165/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=165&range=00
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/lilliput/pull/165.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/165/head:pull/165

PR: https://git.openjdk.org/lilliput/pull/165