Cherry-pick #23686 to 7.x: Fixed reenroll scenario

[michalpristas]

Cherry-pick of PR #23686 to 7.x branch. Original message:

What does this PR do?

Continuation of #23569 on enroll we need to cleanup state otherwise when agent starts it will report unenrolled and fails to proceed with configuration check.

Why is it important?

Reenroll scenario when agent is unenrolled and enrolled later at the time

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Pinging @elastic/agent (Team:Agent)

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: Pull request #23689 opened

• • Start Time: 2021-01-26T14:07:24.709+0000

• Duration: 20 min 1 sec

• Commit: 8a487a0

Test stats 🧪

Test	Results
Failed	0
Passed	1448
Skipped	6
Total	1454

💚 Flaky test report

Tests succeeded.

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Test stats 🧪

Test	Results
Failed	0
Passed	1448
Skipped	6
Total	1454

[EricDavisX]

lgtm; can we run tests?