RFR: 7903373: Add ability to customize test execution using main wrapper plugin [v18]

[Leonid Mesnik]

> The fix adds support of a plugin that customizes test execution.

Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:

  close classloader

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

Changes:
  - all: https://git.openjdk.org/jtreg/pull/136/files
  - new: https://git.openjdk.org/jtreg/pull/136/files/f4e9cc63..2593bc2d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=17
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=16-17

  Stats: 14 lines in 1 file changed: 2 ins; 2 del; 10 mod
  Patch: https://git.openjdk.org/jtreg/pull/136.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/136/head:pull/136

PR: https://git.openjdk.org/jtreg/pull/136