[jdk17u-dev] RFR: 8301167: Update VerifySignedJar to actually exercise and test verification

[Martin Doerr]

Backport of [JDK-8301167](https://bugs.openjdk.org/browse/JDK-8301167). Clean, but deleted jar file differs.

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Commit messages:
 - Backport 05ea083b0563ddacf3e38dc329ba00dc4bac9b29

Changes: https://git.openjdk.org/jdk17u-dev/pull/1648/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1648&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301167
  Stats: 110 lines in 2 files changed: 84 ins; 12 del; 14 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1648.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1648/head:pull/1648

PR: https://git.openjdk.org/jdk17u-dev/pull/1648