:param courseid: the course id of the course
        :raise InvalidNameException, CourseNotFoundException
        :return: the path to the descriptor of the course

def _get_course_descriptor_path(self, courseid):
        """
        :param courseid: the course id of the course
        :raise InvalidNameException, CourseNotFoundException
        :return: the path to the descriptor of the course
        """
        if not id_checker(courseid):
            raise InvalidNameException("Course with invalid name: " + courseid)
        course_fs = self.get_course_fs(courseid)
        if course_fs.exists("course.yaml"):
            return courseid+"/course.yaml"
        if course_fs.exists("course.json"):
            return courseid+"/course.json"
        raise CourseNotFoundException()