fix(panel): case insensitive sort metric sources

Sorts the list of metric sources that is used in dropdown for Panel
Data Source on the Metrics tab so that it is case insensitive and
so that the built data sources are last in the list.

public/app/core/services/datasource_srv.js

@@ -97,10 +97,19 @@ function (angular, _, coreModule, config) {
       }
 
       metricSources.sort(function(a, b) {
-        if (a.meta.builtIn || a.name > b.name) {
+        if (a.meta.builtIn) {
           return 1;
         }
-        if (a.name < b.name) {
+
+        if (b.meta.builtIn) {
+          return -1;
+        }
+
+        if (a.name.toLowerCase() > b.name.toLowerCase()) {
+          return 1;
+        }
+
+        if (a.name.toLowerCase() < b.name.toLowerCase()) {
           return -1;
         }
         return 0;

public/test/specs/datasource_srv_specs.js

+define([
+  'app/core/config',
+  'app/core/services/datasource_srv'
+], function(config) {
+  'use strict';
+
+  describe('datasource_srv', function() {
+    var _datasourceSrv;
+    var metricSources;
+    var templateSrv = {};
+
+    beforeEach(module('grafana.core'));
+    beforeEach(module(function($provide) {
+      $provide.value('templateSrv', templateSrv);
+    }));
+    beforeEach(module('grafana.services'));
+    beforeEach(inject(function(datasourceSrv) {
+      _datasourceSrv = datasourceSrv;
+    }));
+
+    describe('when loading metric sources', function() {
+      var unsortedDatasources = {
+        'mmm': {
+          type: 'test-db',
+          meta: { metrics: {m: 1} }
+        },
+        '--Mixed--': {
+          type: 'test-db',
+          meta: {builtIn: true, metrics: {m: 1} }
+        },
+        'ZZZ': {
+          type: 'test-db',
+          meta: {metrics: {m: 1} }
+        },
+        'aaa': {
+          type: 'test-db',
+          meta: { metrics: {m: 1} }
+        },
+        'BBB': {
+          type: 'test-db',
+          meta: { metrics: {m: 1} }
+        },
+      };
+      beforeEach(function() {
+        config.datasources = unsortedDatasources;
+        metricSources = _datasourceSrv.getMetricSources({skipVariables: true});
+      });
+
+      it('should return a list of sources sorted case insensitively with builtin sources last', function() {
+        expect(metricSources[0].name).to.be('aaa');
+        expect(metricSources[1].name).to.be('BBB');
+        expect(metricSources[2].name).to.be('mmm');
+        expect(metricSources[3].name).to.be('ZZZ');
+        expect(metricSources[4].name).to.be('--Mixed--');
+      });
+    });
+  });
+});