RFR: checkout-bot: support pulling tags

[Erik Helin]

Hi all,

please review this patch that allows the checkout bot to support pulling tags. To achieve this I updated
`Repository.pull` to take an explicit `includeTags` argument.

Testing:
- [x] `make test` passes on Linux x64
- [x] Added a new unit test

Thanks,
Erik

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Commit messages:
 - vcs: support pulling tags

Changes: https://git.openjdk.java.net/skara/pull/819/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=819&range=00
  Stats: 69 lines in 5 files changed: 55 ins; 0 del; 14 mod
  Patch: https://git.openjdk.java.net/skara/pull/819.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/819/head:pull/819

PR: https://git.openjdk.java.net/skara/pull/819