RFR: 8284993: Replace System.exit call in swing tests with RuntimeException

[Prasanta Sadhukhan]

Few swing tests call System.exit() which might stop the test harness from executing further tests if any of the test fail. We should replace with RuntimeException.

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Commit messages:
 - 8284993: Replace System.exit call in swing tests with RuntimeException
 - 8284993: Replace System.exit call in swing tests with RuntimeException

Changes: https://git.openjdk.java.net/jdk/pull/8293/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8293&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284993
  Stats: 6 lines in 6 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8293.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8293/head:pull/8293

PR: https://git.openjdk.java.net/jdk/pull/8293