RFR: 8312474: JFR: Improve logging to diagnose event stream timeout

[Erik Gahlin]

Could I have review of a PR that adds logging to diagnose a test timeout. 

It also fixes a bug where the test didn't wait for the Old Collection event to arrive.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/14960/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14960&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312474
  Stats: 17 lines in 3 files changed: 15 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14960.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14960/head:pull/14960

PR: https://git.openjdk.org/jdk/pull/14960