RFR: 2386: PullRequestBotFactory creates too many IssueBots

[Zhao Song]

Erik found that our bot creates multiple IssueBot instances for a single issue project. And he found that the root cause was the configuration::issueProject method always returning a new instance. Additionally, the equals() and hashcode() methods were not overridden in the JiraProject class.

This patch is trying to fix this issue as Erik suggested:
1. Caching the issueProject instances in a map.
2. Avoiding using IssueProject as a key in maps.

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Commit messages:
 - SKARA-2386

Changes: https://git.openjdk.org/skara/pull/1689/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1689&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2386
  Stats: 22 lines in 1 file changed: 6 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/skara/pull/1689.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1689/head:pull/1689

PR: https://git.openjdk.org/skara/pull/1689