RFR: 1385: Backport MR links to the wrong CSR request

[Guoxiong Li]

Hi all,

This patch solves the wrong CSR in the backport PR. It mainly has the following rules:
1. if the `version` in `.jcheck/conf` doesn't exist or the `version` is wrong, the bot think the CSR also doesn't exist.
2. else, if the `version` in `.jcheck/conf` matches the fix version of the primary CSR, the bot will use the primary CSR. (primary CSR is the CSR of the primary issue)
3. else, if these is a backport issue matches the `version`, the bot will find the CSR of the backport issue. If found, use it. If not, the bot think the CSR doesn't exist.
4. else (no backport issue matches the `version`) the bot think the CSR doesn't exist.

The classes `CSRBot`, `CheckRun` and `CSRCommand` will handle the situations above respectively.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - SKARA-1385

Changes: https://git.openjdk.java.net/skara/pull/1318/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1318&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1385
  Stats: 661 lines in 11 files changed: 631 ins; 1 del; 29 mod
  Patch: https://git.openjdk.java.net/skara/pull/1318.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1318/head:pull/1318

PR: https://git.openjdk.java.net/skara/pull/1318