[Serverless][FTR] Fix flaky viewer_role_login test for MKI (#178522)

Resolves: #178403

Drop wrapper div and place data test subj within the eui component, per
[docs](https://eui.elastic.co/#/navigation/context-menu).

Also:
- add calls to wait until loading has finished
- add 10_000 timeouts to test subects calls

---------

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/security/public/nav_control/nav_control_component.tsx

@@ -179,19 +179,18 @@ export const SecurityNavControl: FunctionComponent<SecurityNavControlProps> = ({
       panelPaddingSize="none"
       buffer={0}
     >
-      <div data-test-subj="userMenu">
-        <EuiContextMenu
-          className="chrNavControl__userMenu"
-          initialPanelId={0}
-          panels={[
-            {
-              id: 0,
-              title: displayName,
-              content: <ContextMenuContent items={items} />,
-            },
-          ]}
-        />
-      </div>
+      <EuiContextMenu
+        className="chrNavControl__userMenu"
+        initialPanelId={0}
+        panels={[
+          {
+            id: 0,
+            title: displayName,
+            content: <ContextMenuContent items={items} />,
+          },
+        ]}
+        data-test-subj="userMenu"
+      />
     </EuiPopover>
   );
 };

x-pack/test_serverless/functional/page_objects/svl_common_page.ts

@@ -11,7 +11,7 @@ export function SvlCommonPageProvider({ getService, getPageObjects }: FtrProvide
   const testSubjects = getService('testSubjects');
   const find = getService('find');
   const config = getService('config');
-  const pageObjects = getPageObjects(['security', 'common']);
+  const pageObjects = getPageObjects(['security', 'common', 'header']);
   const retry = getService('retry');
   const deployment = getService('deployment');
   const log = getService('log');
@@ -229,15 +229,22 @@ export function SvlCommonPageProvider({ getService, getPageObjects }: FtrProvide
     },
 
     async clickUserAvatar() {
-      await testSubjects.click('userMenuAvatar');
+      await pageObjects.header.waitUntilLoadingHasFinished();
+      await testSubjects.click('userMenuAvatar', 10_000);
     },
 
     async assertUserAvatarExists() {
-      await testSubjects.existOrFail('userMenuAvatar');
+      await pageObjects.header.waitUntilLoadingHasFinished();
+      await testSubjects.existOrFail('userMenuAvatar', {
+        timeout: 10_000,
+      });
     },
 
     async assertUserMenuExists() {
-      await testSubjects.existOrFail('userMenu');
+      await pageObjects.header.waitUntilLoadingHasFinished();
+      await testSubjects.existOrFail('userMenu', {
+        timeout: 10_000,
+      });
     },
   };
 }