RFR: 212: Retry notifications for updaters that can check current state

[Robin Westberg]

Hi all,

Please review this change that enables issue notifications to be retried in case transient server errors occur, but will not send out duplicate email notifications.

Best regards,
Robin

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Commits:
 - b78f2a14: Initial implementation

Changes: https://git.openjdk.java.net/skara/pull/339/files
 Webrev: https://webrevs.openjdk.java.net/skara/339/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-212
  Stats: 211 lines in 8 files changed: 181 ins; 7 del; 23 mod
  Patch: https://git.openjdk.java.net/skara/pull/339.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/339/head:pull/339

PR: https://git.openjdk.java.net/skara/pull/339