RFR: 2297: CSRs for OpenJDK 8u backports not being picked up [v2]

[Zhao Song]

> Currently, the version matching logic in `Backports::findClosetIssue` and `Backports::findIssue` differs, causing the skara bot fail to find CSRs for some issues.
> 
> In this patch, I'm trying to unify the version matching logic between the two methods. I couldn't find a good way to reuse the previous methods(`Backports::matchVersion`, `Backports::matchOptPoolVersion`, `Backports::matchPoolVersion`, `Backports::matchScratchVersion`), so I changed the interface of the methods.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  review comment

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Changes:
  - all: https://git.openjdk.org/skara/pull/1661/files
  - new: https://git.openjdk.org/skara/pull/1661/files/8f323b68..2e4ef8cf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1661&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1661&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1661.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1661/head:pull/1661

PR: https://git.openjdk.org/skara/pull/1661