RFR: 8355278: Improve debuggability of com/sun/jndi/ldap/LdapPoolTimeoutTest.java test

[Jaikiran Pai]

Can I please get a review of this test only change which proposes to improve the debuggability of `com/sun/jndi/ldap/LdapPoolTimeoutTest.java`?

This test has been failing intermittently in our CI for several years. Detailed are noted in https://bugs.openjdk.org/browse/JDK-8287062. Most of these failures are because the exception message, in an exception that was raised, contains an unexpected value (apparently `null`). The test doesn't propagate the unexpected exception, thus it's not clear why the exception message is different than what the test expects. The commit in this PR propagates the original exception if the message is unexpected. This should help identify the underlying cause of the test failure, if/when it fails the next time.

I have run this test with these changes and the test continues to pass.

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Commit messages:
 - 8355278: Improve debuggability of com/sun/jndi/ldap/LdapPoolTimeoutTest.java test

Changes: https://git.openjdk.org/jdk/pull/24793/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24793&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355278
  Stats: 25 lines in 1 file changed: 14 ins; 2 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/24793.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24793/head:pull/24793

PR: https://git.openjdk.org/jdk/pull/24793