use methods of kbn to convert interval string to both second and millisecond

public/app/plugins/datasource/elasticsearch/datasource.js

@@ -219,38 +219,9 @@ function (angular, _, moment, kbn, ElasticQueryBuilder, IndexPattern, ElasticRes
         return $q.when([]);
       }
 
-      // convert interval string to milliseconds
-      var intervalToSecond = function (intervalString) {
-        if (!intervalString) {
-          return 1;
-        } else {
-          var interval = parseInt(intervalString);
-          if (isNaN(interval)) {
-            return 1;
-          } else  {
-            var lastIndex = intervalString.length - 1;
-            var unit = intervalString.slice(lastIndex);
-            var scale = 1;
-            switch (unit) {
-              case 'd':
-                scale = 86400;
-                break;
-              case 'h':
-                scale = 3600;
-                break;
-              case 'm':
-                scale = 60;
-                break;
-              default:
-                scale = 1;
-            }
-            return interval * scale;
-          }
-        }
-      };
-
-      // intervalSecond: interval in seconds
-      payload = payload.replace(/\$intervalSecond/g, intervalToSecond(options.interval));
+      // intervalSec: interval in seconds
+      payload = payload.replace(/\$intervalSec/g, kbn.interval_to_seconds(options.interval));
+      payload = payload.replace(/\$intervalMs/g, kbn.interval_to_ms(options.interval));
       payload = payload.replace(/\$interval/g, options.interval);
       payload = payload.replace(/\$timeFrom/g, options.range.from.valueOf());
       payload = payload.replace(/\$timeTo/g, options.range.to.valueOf());