fix(templating): fix to datasource variable, was not updated on dashboard load, added unit test for case as well

public/app/features/templating/datasource_variable.ts

@@ -10,6 +10,7 @@ export class DatasourceVariable implements Variable {
   query: string;
   options: any;
   current: any;
+  refresh: any;
 
  defaults = {
     type: 'datasource',
@@ -20,11 +21,13 @@ export class DatasourceVariable implements Variable {
     regex: '',
     options: [],
     query: '',
+    refresh: 1,
   };
 
   /** @ngInject **/
   constructor(private model, private datasourceSrv, private variableSrv) {
     assignModelProperties(this, model, this.defaults);
+    this.refresh = 1;
   }
 
   getModel() {

public/app/features/templating/specs/variable_srv_init_specs.ts

@@ -62,6 +62,7 @@ describe('VariableSrv init', function() {
           options: [{text: "test", value: "test"}]
         }];
         scenario.urlParams["var-apps"] = "new";
+        scenario.metricSources = [];
       });
 
       it('should update current value', () => {
@@ -110,6 +111,30 @@ describe('VariableSrv init', function() {
     });
   });
 
+  describeInitScenario('when datasource variable is initialized', scenario => {
+    scenario.setup(() => {
+      scenario.variables = [{
+          type: 'datasource',
+          query: 'graphite',
+          name: 'test',
+          current: {value: 'backend4_pee', text: 'backend4_pee'},
+          regex: '/pee$/'
+        }
+      ];
+      scenario.metricSources = [
+        {name: 'backend1', meta: {id: 'influx'}},
+        {name: 'backend2_pee', meta: {id: 'graphite'}},
+        {name: 'backend3', meta: {id: 'graphite'}},
+        {name: 'backend4_pee', meta: {id: 'graphite'}},
+      ];
+    });
+
+    it('should update current value', function() {
+      var variable = ctx.variableSrv.variables[0];
+      expect(variable.options.length).to.be(2);
+    });
+  });
+
   describeInitScenario('when template variable is present in url multiple times', scenario => {
     scenario.setup(() => {
       scenario.variables = [{