* Returns a boolean indicating if the project is the top level project for
     * this reactor build.  The top level project may be different from the
     * {@code rootDirectory}, especially if a subtree of the project is being
     * built, either because Maven has been launched in a subdirectory or using
     * a {@code -f} option.
     *
     * @return {@code true} if the project is the top level project for this build
     */