RFR: 7903507: jtreg runs into race conditions for multi-modules tests

[Christian Stein]

This change puts the necessary JAR files onto the module path as (automatic) modules - without copying them. Therefore, no race condition can happen when multiple tests that require modules of test frameworks are compiling or executing in parallel.

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Commit messages:
 - 7903507: jtreg runs into race conditions for multi-modules tests

Changes: https://git.openjdk.org/jtreg/pull/161/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=161&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903507
  Stats: 67 lines in 2 files changed: 6 ins; 48 del; 13 mod
  Patch: https://git.openjdk.org/jtreg/pull/161.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/161/head:pull/161

PR: https://git.openjdk.org/jtreg/pull/161