function onResponse(rawResponse, flatResponse, error) {
            lastResponse = rawResponse;
            if (userProvidedCallBack) {
                userProvidedCallBack(rawResponse, flatResponse, error);
            }
        }
Converts a RequestPolicy based HttpClient to a PipelineRequest based HttpClient.
@param requestPolicyClient - A HttpClient compatible with core-http
@returns A HttpClient compatible with core-rest-pipeline