RFR: 8276208: vmTestbase/nsk/jdb/repeat/repeat001/repeat001.java fails with "AssertionError: Unexpected output"

[Jakob Cornell]

This will fix a few issues with the tests added in #5290:

- [ ] intermittent failures
- [x] tests should use `failure` method to report problems rather than throwing `AssertionError`

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Commit messages:
 - Use `failure' method instead of `AssertionError' in new tests

Changes: https://git.openjdk.java.net/jdk/pull/6182/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6182&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276208
  Stats: 23 lines in 2 files changed: 1 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6182.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6182/head:pull/6182

PR: https://git.openjdk.java.net/jdk/pull/6182