AMBARI-26529 Fix Kerberos admin session ajax failure (#4039)

* AMBARI-26529 Fix Kerberos admin session ajax failure and avoid unnecessary KERBEROS service deletion

* AMBARI-26529 Added test case and removed Kerberos service check

* Fixed spaces

Author: shubhluck

ambari-web/app/utils/ajax/ajax.js

@@ -37,7 +37,8 @@ var urls = {
     'mock': '/data/wizard/deploy/poll_1.json',
     'format': function (data) {
       return {
-        data: JSON.stringify(data.data)
+        data: JSON.stringify(data.data),
+        dataType: 'text'
       };
     }
   },

ambari-web/test/controllers/main/admin/kerberos/step2_controller_test.js

@@ -838,6 +838,7 @@ describe('App.KerberosWizardStep2Controller', function() {
       expect(args[0]).to.be.eql({
         name: 'common.cluster.update',
         sender: controller,
+        dataType: 'text',
         data: {
           clusterName: 'c1',
           data: [{