Use v8format=true for Kibana health check

[andrewkroh]

What does this PR do?

The default format of the /api/status output is changing so update our
check. We'll use v8format=true so that checks against older images will
pass too.

Relates elastic/kibana#110830

Why is it important?

Allows tests to execute under newer Kibana versions.

Logs

Old format:

{
  "name": "fd1c727b700f",
  "uuid": "903de1b1-9d8b-4db6-9932-00c8ccd26bbc",
  "version": {
    "number": "8.0.0",
    "build_hash": "b1f38f459f9b5f259e9f99ad9d02f67e90505830",
    "build_number": 45390,
    "build_snapshot": true
  },
  "status": {
    "overall": {
      "since": "2021-09-29T13:46:24.658Z",
      "state": "yellow",
      "title": "Yellow",
      "nickname": "I'll be back",
      "icon": "warning",
      "uiColor": "warning"
    },

New format:

{
  "name": "7d1500db67ba",
  "uuid": "d55b6d6c-0b87-4364-915f-cc92af242a67",
  "version": {
    "number": "8.0.0",
    "build_hash": "c647929eeb7881bf3f80dcc1d4dab0027650666e",
    "build_number": 46558,
    "build_snapshot": true
  },
  "status": {
    "overall": {
      "level": "available",
      "summary": "All services are available"
    },
    "core": {
      "elasticsearch": {
        "level": "available",
        "summary": "Elasticsearch is available",
        "meta": {
          "warningNodes": [],
          "incompatibleNodes": []
        }
      },
      "savedObjects": {
        "level": "available",
        "summary": "SavedObjects service has completed migrations and is available",
        "meta": {
          "migratedIndices": {
            "migrated": 0,
            "skipped": 0,
            "patched": 2
          }
        }
      }
    },

[mergify]

This pull request does not have a backport label. Could you fix it @andrewkroh? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[ruflin]

LGTM assuming CI goes green.

[elasticmachine]

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Build stats

• Start Time: 2021-09-29T13:59:42.413+0000

• Duration: 157 min 9 sec

• Commit: 1d4d7bf

Test stats 🧪

Test	Results
Failed	0
Passed	54147
Skipped	5328
Total	59475

💚 Flaky test report

Tests succeeded.

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