RFR: 8339261: Logs truncated in test javax/net/ssl/DTLS/DTLSRehandshakeTest.java

[Fernando Guallini]

The test javax/net/ssl/DTLS/DTLSRehandshakeTest.java runs multiple scenarios, generating a large amount of logging as a result. Since Jtreg truncates the output when it becomes too large, the logs are often not useful for debugging in case of failure.

This PR updates the test to also write the full output to an external file. That will help with debugging this test's occasional failures.

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Commit messages:
 - also writing err to file
 - throw IOexception instead of catching
 - add comment for explanation
 - write logs to an external file

Changes: https://git.openjdk.org/jdk/pull/20838/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20838&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339261
  Stats: 50 lines in 1 file changed: 47 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20838.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20838/head:pull/20838

PR: https://git.openjdk.org/jdk/pull/20838