RFR: 2568: Add more loggings to investigate SKARA-2544

[Zhao Song]

To investigate [SKARA-2544](https://bugs.openjdk.org/browse/SKARA-2544), add more logging in pullRequestPoller

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Commit messages:
 - update
 - SKARA-2568

Changes: https://git.openjdk.org/skara/pull/1734/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1734&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2568
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1734.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1734/head:pull/1734

PR: https://git.openjdk.org/skara/pull/1734