RFR: 8316964: Security tools should not call System.exit [v3]

[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.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  typo

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15951/files
  - new: https://git.openjdk.org/jdk/pull/15951/files/ed6d72c7..e22257a9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15951&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15951&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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