RFR: 7903443: Propagate verbose flag to agents [v3]

[Christian Stein]

> Please review this change to make `jtreg` propagate its verbosity configuration to agents.
> 
> This pull request also updates the `JUnitRunner` agent to evaluate the verbosity configuration and act accordingly.
> For example, passing `-v:nopass,error,fail` at the command line to `jtreg` will suppress the `STARTED: ...` and `SUCCESSFUL: ...` lines in `.jtr` files for JUnit-based tests.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Revert changes in JarManager; they are unrelated

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/187/files
  - new: https://git.openjdk.org/jtreg/pull/187/files/ccbbd1f0..f531969c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=187&range=02
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=187&range=01-02

  Stats: 8 lines in 1 file changed: 1 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jtreg/pull/187.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/187/head:pull/187

PR: https://git.openjdk.org/jtreg/pull/187