Look at the results from the http request instead of checking that the

json matches an md5 hash. This was causing flaky tests because the
order of the users in the test doing `curl -s localhost:9200/_xpack/security/user -u
es_admin:changeMeAgain` is not consistent which caused random failures.
Now if it does fail we will actually know the reason why:
```
 security users
    should have the elastic user
    should have the kibana user (FAILED - 1)
    should have the kibana_server user
    should have the logstash user
  logstash_system access check
    should be reported as version 6.2.4

Failures:

  1) Xpack Tests security users should have the kibana user
     Failure/Error: expect(result['kibana']['username']).to eq('kibana4')

       expected: "kibana4"
            got: "kibana"
```

The failure output use to look like:

```
Failures:

  1) Xpack Tests Command "curl -s localhost:9200/_xpack/security/user -u es_admin:changeMeAgain | md5sum | grep b6a1293c343e745a508c74778c9be8bb" exit_status should eq 0
     Failure/Error: its(:exit_status) { should eq 0 }

       expected: 0
            got: 1

       (compared using ==)
       /bin/sh -c curl\ -s\ localhost:9200/_xpack/security/user\ -u\ es_admin:changeMeAgain\ \|\ md5sum\ \|\ grep\ b6a1293c343e745a508c74778c9be8bb
```

test/integration/helpers/serverspec/xpack_spec.rb

@@ -148,11 +148,6 @@ shared_examples 'xpack::init' do |vars|
   end
 
 
-  #Test native roles and users are loaded
-  describe command('curl -s localhost:9200/_xpack/security/user -u es_admin:changeMeAgain | md5sum | grep b6a1293c343e745a508c74778c9be8bb') do
-    its(:exit_status) { should eq 0 }
-  end
-
   describe 'security roles' do
     it 'should list the security roles' do
       roles = curl_json('http://localhost:9200/_xpack/security/role', username='es_admin', password='changeMeAgain')
@@ -227,11 +222,30 @@ shared_examples 'xpack::init' do |vars|
     end
   end
 
-  describe command('curl -s localhost:9200/_xpack/security/user/kibana4_server -u elastic:elasticChanged | md5sum | grep f0548742161d9e50c7c7fbe2e061a1fa') do
-      its(:exit_status) { should eq 0 }
+  describe 'security users' do
+    result = curl_json('http://localhost:9200/_xpack/security/user', username='elastic', password='elasticChanged')
+    it 'should have the elastic user' do
+      expect(result['elastic']['username']).to eq('elastic')
+      expect(result['elastic']['roles']).to eq(['superuser'])
+      expect(result['elastic']['enabled']).to eq(true)
+    end
+    it 'should have the kibana user' do
+      expect(result['kibana']['username']).to eq('kibana')
+      expect(result['kibana']['roles']).to eq(['kibana_system'])
+      expect(result['kibana']['enabled']).to eq(true)
+    end
+    it 'should have the kibana_server user' do
+      expect(result['kibana4_server']['username']).to eq('kibana4_server')
+      expect(result['kibana4_server']['roles']).to eq(['kibana4_server'])
+      expect(result['kibana4_server']['enabled']).to eq(true)
+    end
+    it 'should have the logstash user' do
+      expect(result['logstash_system']['username']).to eq('logstash_system')
+      expect(result['logstash_system']['roles']).to eq(['logstash_system'])
+      expect(result['logstash_system']['enabled']).to eq(true)
+    end
   end
 
-
   describe 'logstash_system access check' do
     it 'should be reported as version '+vars['es_version'] do
       command = command('curl -s localhost:9200/ -u logstash_system:aNewLogstashPassword | grep number')
@@ -240,10 +254,6 @@ shared_examples 'xpack::init' do |vars|
     end
   end
 
-  describe command('curl -s localhost:9200/_xpack/security/user/logstash_system -u elastic:elasticChanged | md5sum | grep 98d361ddfa5156abd33542a493b4fd85') do
-      its(:exit_status) { should eq 0 }
-  end
-
   if vars['es_major_version'] == '5.x' # kibana default password has been removed in 6.x
     describe 'kibana access check' do
       it 'should be reported as version '+vars['es_version'] do
@@ -252,10 +262,5 @@ shared_examples 'xpack::init' do |vars|
       end
     end
   end
-
-  describe command('curl -s localhost:9200/_xpack/security/user/kibana -u elastic:elasticChanged | md5sum | grep 34190c64eb3c7cfb002fa789df5fad20') do
-      its(:exit_status) { should eq 0 }
-  end
-
 end