RFR: 1706: Store github checks in PR unique way

[Zhao Song]

Currently, checks in GitHub are stored in the commit. So if multiple PRs share the same source commit, then they will compete with the check-runs and store their different checksum in there. This in turn means that all, or most of those PRs will always think the check is outdated when a CheckRun is performed next.
 
This patch adds repository name and pull request id to the name of check in Github. Therefore, even if multiple PRs share the same source commit, every PR will store a unique check in the commit and there is no competition exists.

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Commit messages:
 - SKARA-1706

Changes: https://git.openjdk.org/skara/pull/1470/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1470&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1706
  Stats: 7 lines in 3 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/skara/pull/1470.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1470/head:pull/1470

PR: https://git.openjdk.org/skara/pull/1470