RFR: 8316964: Security tools should not call System.exit

[Weijun Wang]

Remove most `System.exit()` calls in various security tools and only leave one in the `main` method. This paves the way to convert them to JSR 199 tools.

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Commit messages:
 - the fix

Changes: https://git.openjdk.org/jdk/pull/15951/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15951&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316964
  Stats: 480 lines in 8 files changed: 286 ins; 107 del; 87 mod
  Patch: https://git.openjdk.org/jdk/pull/15951.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15951/head:pull/15951

PR: https://git.openjdk.org/jdk/pull/15951