RFR: Better retry logic for the mlbridge archiver

[Robin Westberg]

If the mlbridge fails to push to the archive, it should not try to recreate the commit after rebase.

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Commit messages:
 - Better retry logic

Changes: https://git.openjdk.java.net/skara/pull/896/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=896&range=00
  Stats: 131 lines in 3 files changed: 120 ins; 9 del; 2 mod
  Patch: https://git.openjdk.java.net/skara/pull/896.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/896/head:pull/896

PR: https://git.openjdk.java.net/skara/pull/896