RFR: 8261: Use test flag to skip JDP multicast tests in JolokiaTest [v2]

[Martin Skarsaune]

> I just became aware that there is a new flag used to skip JDP tests. 
> I previously added some env checking to skip similar multicast tests for Jolokia. 
> Hence it would be a lot cleaner to use the new standardized mechanism for this.
> Trying out whether this fixes [JMC-8261](https://bugs.openjdk.org/browse/JMC-8261)

Martin Skarsaune has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into use_new_test_flag_to_avoid_jolokia_discovery
 - Try to use new test flag to decide whether multicast is supported

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

Changes:
  - all: https://git.openjdk.org/jmc/pull/588/files
  - new: https://git.openjdk.org/jmc/pull/588/files/9f8dd613..5b20ff65

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=588&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=588&range=00-01

  Stats: 2268 lines in 291 files changed: 1716 ins; 95 del; 457 mod
  Patch: https://git.openjdk.org/jmc/pull/588.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/588/head:pull/588

PR: https://git.openjdk.org/jmc/pull/588