Copy esArchiver commands from ./reassign.ts to fix tests (#97012) (#9…

…7037)

## Summary

Seeing failures like this locally for `x-pack/test/fleet_api_integration/apis/agents/unenroll.ts` tests
<details><summary>screenshot of error</summary>
<img width="1121" alt="Screen Shot 2021-04-13 at 10 06 51 AM" src="https://user-images.githubusercontent.com/57655/114592495-fec04280-9c58-11eb-939c-b84aa7469c2a.png">
</details>
Copied the `esArchiver` patterns from `x-pack/test/fleet_api_integration/apis/agents/reassign.ts` in #96837 and the error is gone

### Checklist
- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

Co-authored-by: John Schulz <john.schulz@elastic.co>

x-pack/test/fleet_api_integration/apis/agents/unenroll.ts

@@ -23,10 +23,12 @@ export default function (providerContext: FtrProviderContext) {
     let accessAPIKeyId: string;
     let outputAPIKeyId: string;
     before(async () => {
-      await esArchiver.load('fleet/agents');
+      await esArchiver.load('fleet/empty_fleet_server');
     });
     setupFleetAndAgents(providerContext);
     beforeEach(async () => {
+      await esArchiver.unload('fleet/empty_fleet_server');
+      await esArchiver.load('fleet/agents');
       const { body: accessAPIKeyBody } = await esClient.security.createApiKey({
         body: {
           name: `test access api key: ${uuid.v4()}`,
@@ -63,8 +65,12 @@ export default function (providerContext: FtrProviderContext) {
         },
       });
     });
-    after(async () => {
+    afterEach(async () => {
       await esArchiver.unload('fleet/agents');
+      await esArchiver.load('fleet/empty_fleet_server');
+    });
+    after(async () => {
+      await esArchiver.unload('fleet/empty_fleet_server');
     });
 
     it('/agents/{agent_id}/unenroll should fail for managed policy', async () => {