RFR: 7903373: Add ability to customize test execution using main wrapper plugin [v6]

[Leonid Mesnik]

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

Leonid Mesnik has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 45 commits:

 - Merge branch 'loom' of https://github.com/lmesnik/jtreg into loom
 - empty lines removed.
 - year updated.
 - minor cleanup
 - fixes
 - Merge branch 'master' of https://github.com/openjdk/jtreg into loom
 - argumetns added
 - test fixed
 - fixed space
 - more identation fixes
 - ... and 35 more: https://git.openjdk.org/jtreg/compare/0bb8367d...21ea16b6

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Changes: https://git.openjdk.org/jtreg/pull/136/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=136&range=05
  Stats: 451 lines in 16 files changed: 435 ins; 0 del; 16 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