works, afaict. no tests. one TS issue.

```
  firstSuccessOrTryAgain
    ✓ reject/throws is called again & its value returned (18ms)
    ✓ the first success value is cached (2ms)
```

Terrible tests. Committing & pushing to see if it fixes failures like https://github.com/elastic/kibana/pull/74507/checks?check_run_id=980178887

https://kibana-ci.elastic.co/job/elastic+kibana+pipeline-pull-request/67892/execution/node/663/log/

```
07:36:56               └-> "before all" hook
07:36:56               └-> should not allow to enroll an agent with a invalid enrollment
07:36:56                 └-> "before each" hook: global before each
07:36:56                 └-> "before each" hook: beforeSetupWithDockerRegistry
07:36:56                 │ proc [kibana]  error  [11:36:56.369]  Error: Internal Server Error
07:36:56                 │ proc [kibana]     at HapiResponseAdapter.toError (/dev/shm/workspace/parallel/5/kibana/build/kibana-build-xpack/src/core/server/http/router/response_adapter.js:132:19)
07:36:56                 │ proc [kibana]     at HapiResponseAdapter.toHapiResponse (/dev/shm/workspace/parallel/5/kibana/build/kibana-build-xpack/src/core/server/http/router/response_adapter.js:86:19)
07:36:56                 │ proc [kibana]     at HapiResponseAdapter.handle (/dev/shm/workspace/parallel/5/kibana/build/kibana-build-xpack/src/core/server/http/router/response_adapter.js:81:17)
07:36:56                 │ proc [kibana]     at Router.handle (/dev/shm/workspace/parallel/5/kibana/build/kibana-build-xpack/src/core/server/http/router/router.js:164:34)
07:36:56                 │ proc [kibana]     at process._tickCallback (internal/process/next_tick.js:68:7)
07:36:56                 │ proc [kibana]   log   [11:36:56.581] [info][authentication][plugins][security] Authentication attempt failed: [security_exception] missing authentication credentials for REST request [/_security/_authenticate], with { header={ WWW-Authenticate={ 0="ApiKey" & 1="Basic realm=\"security\" charset=\"UTF-8\"" } } }
07:36:56                 └- ✓ pass  (60ms) "Ingest Manager Endpoints Fleet Endpoints fleet_agents_enroll should not allow to enroll an agent with a invalid enrollment"
07:36:56               └-> should not allow to enroll an agent with a shared id if it already exists
07:36:56                 └-> "before each" hook: global before each
07:36:56                 └-> "before each" hook: beforeSetupWithDockerRegistry
07:36:56                 └- ✓ pass  (111ms) "Ingest Manager Endpoints Fleet Endpoints fleet_agents_enroll should not allow to enroll an agent with a shared id if it already exists "
07:36:56               └-> should not allow to enroll an agent with a version > kibana
07:36:56                 └-> "before each" hook: global before each
07:36:56                 └-> "before each" hook: beforeSetupWithDockerRegistry
07:36:56                 └- ✓ pass  (58ms) "Ingest Manager Endpoints Fleet Endpoints fleet_agents_enroll should not allow to enroll an agent with a version > kibana"
07:36:56               └-> should allow to enroll an agent with a valid enrollment token
07:36:56                 └-> "before each" hook: global before each
07:36:56                 └-> "before each" hook: beforeSetupWithDockerRegistry
07:36:56                 └- ✖ fail: Ingest Manager Endpoints Fleet Endpoints fleet_agents_enroll should allow to enroll an agent with a valid enrollment token
07:36:56                 │      Error: expected 200 "OK", got 500 "Internal Server Error"
07:36:56                 │       at Test._assertStatus (/dev/shm/workspace/kibana/node_modules/supertest/lib/test.js:268:12)
07:36:56                 │       at Test._assertFunction (/dev/shm/workspace/kibana/node_modules/supertest/lib/test.js:283:11)
07:36:56                 │       at Test.assert (/dev/shm/workspace/kibana/node_modules/supertest/lib/test.js:173:18)
07:36:56                 │       at assert (/dev/shm/workspace/kibana/node_modules/supertest/lib/test.js:131:12)
07:36:56                 │       at /dev/shm/workspace/kibana/node_modules/supertest/lib/test.js:128:5
07:36:56                 │       at Test.Request.callback (/dev/shm/workspace/kibana/node_modules/superagent/lib/node/index.js:718:3)
07:36:56                 │       at parser (/dev/shm/workspace/kibana/node_modules/superagent/lib/node/index.js:906:18)
07:36:56                 │       at IncomingMessage.res.on (/dev/shm/workspace/kibana/node_modules/superagent/lib/node/parsers/json.js:19:7)
07:36:56                 │       at endReadableNT (_stream_readable.js:1145:12)
07:36:56                 │       at process._tickCallback (internal/process/next_tick.js:63:19)
07:36:56                 │
07:36:56                 │
```

`firstPromiseBlocksAndFufills` for "the first promise created blocks others from being created, then fufills all with that first result"

Add explicit `isPending` value instead of overloading role of `status`. Could probably do without it, but it makes the intent more clear.

…ailed-setup