Don't retry on http status codes >= 300

These status codes are likely to be to be unretryable errors coming from
influx (most likely bad queries)

src/app/services/influxdb/influxdbDatasource.js

@@ -131,12 +131,14 @@ function (angular, _, kbn) {
 
     function retry(deferred, callback, delay) {
       return callback().then(undefined, function(reason) {
-        if (reason.status !== 0) {
+        if (reason.status !== 0 || reason.status >= 300) {
           deferred.reject(reason);
         } 
+        else {
           setTimeout(function() {
             return retry(deferred, callback, Math.min(delay * 2, 30000));
           }, delay);
+        }
       });
     }