def extra_branches
      case branch_type
      when Git::DEPLOYABLE_PREFIX, Git::STAGING_PREFIX, Git::QAREADY_PREFIX
        Git.branches_for(branch_type) - [branch_name]
      else
        raise InvalidBranchType, "'#{branch_type}' is not a valid branch type"
      end
    end
def extra_branches
      case branch_type
      when Git::DEPLOYABLE_PREFIX, Git::STAGING_PREFIX, Git::QAREADY_PREFIX
        Git.branches_for(branch_type) - [branch_name]
      else
        raise InvalidBranchType, "'#{branch_type}' is not a valid branch type"
      end
    end
Public: The list of extra branches that exist after creating the new branch

 Returns an Array of Strings of the branch names