Make min period as 12 hours

because we only collect disk data twice a day

src/views/app.html

@@ -822,7 +822,7 @@
                 <span class="caret"></span>
               </button>
               <ul class="dropdown-menu">
-                <li><a href="" ng-click="graphs.setPeriod(6, '6 hours')">6 hours</a></li>
+                <li><a href="" ng-click="graphs.setPeriod(12, '12 hours')">12 hours</a></li>
                 <li><a href="" ng-click="graphs.setPeriod(24, '24 hours')">24 hours</a></li>
                 <li><a href="" ng-click="graphs.setPeriod(24*7, '7 days')">7 days</a></li>
                 <li><a href="" ng-click="graphs.setPeriod(24*30, '30 days')">30 days</a></li>

src/views/app.js

@@ -593,8 +593,8 @@ angular.module('Application').controller('AppController', ['$scope', '$location'
     $scope.graphs = {
         error: {},
 
-        period: 6,
-        periodLabel: '6 hours',
+        period: 12, // set as 12 because disk graphs is only collected twice a day
+        periodLabel: '12 hours',
         memoryChart: null,
         diskChart: null,