RFR: 8284: Fix Jolokia discovery issues [v2]

[Martin Skarsaune]

> This fixes two bugs with Jolokia discovery:
> 1. serious : repeated discovery runs crash. Runing repeatedly in the background is the whole point
> 2. more of an annoyance: the PR disables JMC agent by omitting JVM info in the descriptor (as presence is interpreted as a local JVM)
> Both tested OK.

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 four additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into jolokia_discovery_issues
 - reverted file that was committed by error
 - Remove JVM info on discovered Jolokia VMs in order to disable JMC Agent functionality
 - Fix bug where repeated runs of discovery crashes (kind of a showstopper)

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

Changes:
  - all: https://git.openjdk.org/jmc/pull/597/files
  - new: https://git.openjdk.org/jmc/pull/597/files/b29d9841..21515ce8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=597&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=597&range=00-01

  Stats: 141 lines in 5 files changed: 131 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jmc/pull/597.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/597/head:pull/597

PR: https://git.openjdk.org/jmc/pull/597