RFR: 1384: Cannot configure integrators for repositories in PullRequestBot

[Zhao Song]

Now, `PullRequestBotFactory` could parse the config `integrators`.

Also fixed some whitespace issues in `PullRequestBotFactoryTest`

-------------

Commit messages:
 - SKARA-1384

Changes: https://git.openjdk.org/skara/pull/1402/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1402&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1384
  Stats: 22 lines in 2 files changed: 15 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/skara/pull/1402.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1402/head:pull/1402

PR: https://git.openjdk.org/skara/pull/1402