Test: fix kibana write rolling upgrade test

This commit fixes the kibana write rolling upgrade test. The test needs to enable the kibana user
as another test explicitly disables it. After the test runs it disables the kibana user again.

relates elastic/x-pack-elasticsearch#1460

Original commit: elastic/x-pack-elasticsearch@437495432d

qa/rolling-upgrade/build.gradle

@@ -103,7 +103,6 @@ for (Version version : wireCompatVersions) {
   Task mixedClusterTestRunner = tasks.getByName("${baseName}#mixedClusterTestRunner")
   mixedClusterTestRunner.configure {
     systemProperty 'tests.rest.suite', 'mixed_cluster'
-    systemProperty 'tests.rest.blacklist', 'mixed_cluster/30_kibana_write/*'
     finalizedBy "${baseName}#oldClusterTestCluster#node0.stop"
   }
 

qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/30_kibana_write.yml

@@ -1,4 +1,44 @@
 ---
+setup:
+  - do:
+      cluster.health:
+        wait_for_status: yellow
+        wait_for_nodes: 2
+        timeout: 25s
+
+  - do:
+      update:
+        index: ".security"
+        type: "reserved-user"
+        id: "kibana"
+        refresh: true
+        body: >
+          {
+            "doc": {
+              "enabled": true
+            }
+          }
+  - do:
+      xpack.security.clear_cached_realms:
+        realms: "_all"
+---
+teardown:
+  - do:
+      update:
+        index: ".security"
+        type: "reserved-user"
+        id: "kibana"
+        refresh: true
+        body: >
+          {
+            "doc": {
+              "enabled": false
+            }
+          }
+  - do:
+      xpack.security.clear_cached_realms:
+        realms: "_all"
+---
 "Verify kibana user role works in mixed cluster":
   - do:
       headers:
@@ -14,11 +54,6 @@
        Authorization: "Basic a2liYW5hOmNoYW5nZW1l"
      indices.create:
        index: .kibana-foo
-       wait_for_active_shards : all
-       body:
-         settings:
-           index:
-             number_of_replicas: 1
 
   - do:
      headers: