RFR: 2038: Don't post error message of invalid jcheck configuration when encountering UncheckedIOException

[Zhao Song]

In CheckWorkItem, the bot would check whether this pull request has a valid jcheck configuration and if not, the bot would post an error message of invalid jcheck configuration in the pull request. 

Today, a user reported that he saw this error message in his pull request and he couldn't determine whether the pull request is good. After reading the log, I found that it's just a temporary glitch. The bot was trying to read jcheck configuration in GitHub but got HttpTimeoutException, so the bot posted the error message. But it recovers in the next try. 
https://github.com/openjdk/panama-foreign/pull/893 

To sum, in the cases of some temporary glitches, we shouldn't post error message to pull request to confuse users.

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Commit messages:
 - SKARA-2038

Changes: https://git.openjdk.org/skara/pull/1559/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1559&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2038
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1559.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1559/head:pull/1559

PR: https://git.openjdk.org/skara/pull/1559