private <T> void addCustomData(List<T> list, int index, T[] data) {
		if (data.length > index) {
			list.add(data[index]);
		}
	}
Get system monitor data and wrap the data as a string value like "[22,11,12,34,....]", which can be used directly
in JS as a vector.

@param testId       test id
@param targetIP     ip address of the monitor target
@param dataInterval interval value to get data. Interval value "2" means, get one record for every "2" records.
@return return the data in map
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java