public int getReportPluginGraphInterval(long testId, String plugin, String kind, int imageWidth) {
		return getRecordInterval(imageWidth, getReportPluginDataFile(testId, plugin, kind));
	}
Get interval value of the monitor data of a plugin, like jvm monitor plugin.
The usage of interval value is same as system monitor data.

@param testId     test id
@param plugin     plugin name
@param kind       plugin kind
@param imageWidth image with of the chart.
@return interval value.
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java