RFR: 7903373: Add ability to customize test execution using main wrapper plugin [v19]

[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:

  better error handling

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

Changes:
  - all: https://git.openjdk.org/jtreg/pull/136/files
  - new: https://git.openjdk.org/jtreg/pull/136/files/2593bc2d..d114d9c4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=18
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=17-18

  Stats: 9 lines in 1 file changed: 3 ins; 1 del; 5 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