RFR: 8286460: Remove dependence on JAR filename in CDS tests

[Christian Stein]

Use location information stored in JUnit `Test` class' runtime representation in order to remove a hard-coded dependence on JUnit's JAR filename.

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Commit messages:
 - 8286460: Remove dependence on JAR filename in CDS tests

Changes: https://git.openjdk.java.net/jdk/pull/8624/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8624&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286460
  Stats: 112 lines in 14 files changed: 0 ins; 98 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8624.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8624/head:pull/8624

PR: https://git.openjdk.java.net/jdk/pull/8624