Fix Grafana 4 showing an error on empty result for live stat
Fix Grafana 4 showing an error on empty result for live stat

(tested with Grafana 4 beta 2)
=> on empty result, return an empty array (rather than a singleton array containing itself an empty array, as before)

Note that this fix is compliant with Grafana 3.x

hawkular/hawkular-grafana-datasource,jotak/hawkular-grafana-datasource,hawkular/hawkular-grafana-datasource,jotak/hawkular-grafana-datasource,hawkular/hawkular-grafana-datasource,jotak/hawkular-grafana-datasource