RFR: 7903519 : jtreg/jtharness is missing features for basic crash testing

[andrlos]

provides SPI for enabling external status transformations of failed tests

this is a continuation of efforts after https://github.com/openjdk/jtharness/pull/59 

Requires newest jtharness build (not even tagged yet) that includes above mentioned change to be compiled succesfully

The main idea is to provide a unified StatusTransformer interface, that can be externally implemented by users and added to a classpath in a separate jar to allow modifications of test execution status based on some elementary analysis. This can be easily used for crashtesting (filtering out only tests with jvm crashes).

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Commit messages:
 - SPI for enabling external status transformations of failed tests

Changes: https://git.openjdk.org/jtreg/pull/235/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=235&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903519
  Stats: 94 lines in 2 files changed: 94 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/235.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/235/head:pull/235

PR: https://git.openjdk.org/jtreg/pull/235