RFR: 1932: Override abstract method canCreatePullRequest in BitbucketRepository

[Zhao Song]

After integrated [SKARA-1903](https://bugs.openjdk.org/browse/SKARA-1903), the build of SKARA failed. The reason is that BitbucketRepository implements interface HostedRepository and in [SKARA-1903](https://bugs.openjdk.org/browse/SKARA-1903), a new method canCreatePullRequest was introduced in HostedRepository, so we need to override this method in BitbucketRepository.

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Commit messages:
 - SKARA-1932

Changes: https://git.openjdk.org/skara/pull/1525/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1525&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1932
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1525.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1525/head:pull/1525

PR: https://git.openjdk.org/skara/pull/1525