RFR: 7903373: Add ability to customize test execution using main wrapper plugin [v7]

[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:

  Exceptions catching fixed.

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/136/files
  - new: https://git.openjdk.org/jtreg/pull/136/files/21ea16b6..8d62ef99

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=06
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=05-06

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 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