Fixes for SNAP-2422: (#112)

  - Code changes for displaying error message if loading Google charts library fails.
  - Code changes for retrying loading of Google charts library.
  - Update Auto-Refresh error message to guide user to go to lead logs if there is any connectivity issue.

Author: snappy-sachin

core/src/main/resources/org/apache/spark/ui/static/snappydata/snappy-commons.js

@@ -140,5 +140,7 @@ var ajaxRequestErrorHandler = function (jqXHR, status, error) {
     displayMessage += status + " : "+error;;
   }
 
+  displayMessage += "<br>Please check lead logs to know more.";
+
   $("#AutoUpdateErrorMsg").html(displayMessage).show();
 }

core/src/main/resources/org/apache/spark/ui/static/snappydata/snappy-dashboard.js

@@ -1,4 +1,5 @@
 
+var isGoogleChartLoaded = false;
 var isMemberCellExpanded = {};
 
 function updateCoreDetails(coresInfo) {
@@ -351,6 +352,14 @@ function getExternalTableStatsGridConf() {
 }
 
 function updateUsageCharts(statsData){
+
+  // Load charts library if not already loaded
+  if(!isGoogleChartLoaded) {
+    // Set error message
+    $("#googleChartsErrorMsg").show();
+    return;
+  }
+
   var cpuChartData = new google.visualization.DataTable();
   cpuChartData.addColumn('datetime', 'Time of Day');
   cpuChartData.addColumn('number', 'CPU');
@@ -457,16 +466,35 @@ function updateUsageCharts(statsData){
     diskSpaceUsageChart.draw(diskSpaceUsageChartData, diskSpaceUsageChartOptions);
 }
 
-function loadGoogleCharts(){
-  google.charts.load('current', {'packages':['corechart']});
-  google.charts.setOnLoadCallback(googleChartsLoaded);
+function loadGoogleCharts() {
+
+  if((typeof google === 'object' && typeof google.charts === 'object')) {
+    $("#googleChartsErrorMsg").hide();
+    google.charts.load('current', {'packages':['corechart']});
+    google.charts.setOnLoadCallback(googleChartsLoaded);
+    isGoogleChartLoaded = true;
+  } else {
+    $("#googleChartsErrorMsg").show();
+  }
+
 }
 
-function googleChartsLoaded(){
+function googleChartsLoaded() {
   loadClusterInfo();
 }
 
 function loadClusterInfo() {
+
+  if(!isGoogleChartLoaded) {
+    $.ajax({
+      url: "https://www.gstatic.com/charts/loader.js",
+      dataType: "script",
+      success: function() {
+        loadGoogleCharts()
+      }
+    });
+  }
+
   $.ajax({
     url:"/snappy-api/services/clusterinfo",
     dataType: 'json',