RFR: 1625: Validate input from /summary command

[Zhao Song]

1.  Added validation to SummaryCommand.
2. If exceptions are thrown when the bot is evaluating the current status of the pr, the exceptions will be treated as integration blocker.

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Commit messages:
 - Merge branch 'master' into SKARA-1625
 - SKARA-1625

Changes: https://git.openjdk.org/skara/pull/1401/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1401&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1625
  Stats: 83 lines in 3 files changed: 69 ins; 5 del; 9 mod
  Patch: https://git.openjdk.org/skara/pull/1401.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1401/head:pull/1401

PR: https://git.openjdk.org/skara/pull/1401