RFR: JDK-8304171: Fix layout of JCov instrumented bundle on Mac OS

[Alexandre Iline]

Now on all platforms the JCov bundle would look the same.

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Commit messages:
 - JDK-8304171: Fix layout of JCov instrumented bundle on Mac OS

Changes: https://git.openjdk.org/jdk/pull/13027/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13027&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304171
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13027.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13027/head:pull/13027

PR: https://git.openjdk.org/jdk/pull/13027