'Return URL for storing grades.
To test LTI on sandbox we must use http scheme.
While testing locally and on Jenkins, mock_lti_server use http.referer
to obtain scheme, so it is ok to have http(s) anyway.
The scheme logic is handled in lms/lib/xblock/runtime.py'

def get_outcome_service_url(self, service_name='grade_handler'):

    return self.runtime.handler_url(self, service_name, thirdparty=True).rstrip('/?')
