RFR: The checkout method should always checkout what was fetched

[Robin Westberg]

The checkout method of HostedRepositoryPool should always checkout what was just fetched, to ensure no local ref
interferes.

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Commit messages:
 - The checkout method should always checkout what was fetched

Changes: https://git.openjdk.java.net/skara/pull/880/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=880&range=00
  Stats: 57 lines in 2 files changed: 55 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/880.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/880/head:pull/880

PR: https://git.openjdk.java.net/skara/pull/880