Add Gitlab::Git::Repository#branches spec
Use Rugged::Referenc#branch? instead of RegExp matching ref name
Merge branch 'feature/branches_test' of https://github.com/edvakf/gitlab_git into edvakf-feature/branches_test
Update tests

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'edvakf-feature/branches_test'