attachEventOnce(sEventName, fnCallback, oContext) {
							function fnOnce(...aArgs) {
								mService.detachEvent(sEventName, fnOnce);
								fnCallback.apply(oContext, aArgs);
							}
							mService.attachEvent(sEventName, fnOnce);
						}
Returns an RTA service
@param {string} sServiceName - RTA service name to be requested
@returns {Promise} - resolves with a service object