RFR: 6890: defineEventProbes should throw exception on malformed probe definitions

[Joshua Matsuoka]

This PR addresses JMC-6890 (defineEventProbes should throw exception on malformed probe definitions) [1]. Previously the exception would be swallowed by DefaultTransformRegistry when the XML failed validation, and would simply return null. With this change the exception is rethrown and can be handled accordingly by the AgentController, which rethrows it, and the user. I've added a test for the AgentController and updated the test for DefaultTransformRegistry accordingly.

[1] https://bugs.openjdk.java.net/browse/JMC-6890

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Commit messages:
 - 6890: defineEventProbes should throw exception on malformed probe definitions

Changes: https://git.openjdk.java.net/jmc/pull/227/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=227&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6890
  Stats: 38 lines in 5 files changed: 26 ins; 1 del; 11 mod
  Patch: https://git.openjdk.java.net/jmc/pull/227.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/227/head:pull/227

PR: https://git.openjdk.java.net/jmc/pull/227