Cherry-pick #25854 to 7.x: Fix invalid log level sent to endpoint

[michalpristas]

Cherry-pick of PR #25854 to 7.x branch. Original message:

What does this PR do?

The issue is described here #25583 and happens only on low spec environments.
Difficult to reproduce locally. QA is usually successful with this.

I believe there's a race in read-write files in between enroll, run where FS is a bit slower than our process.
Similar issue was fixed here: #24504
Solving this by syncing config files after each write so changes are present on Filesystem immediately.

Why is it important?

Without this agent reports empty log level as desired to endpoint

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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Build stats

• Build Cause: Pull request #25993 opened

• Start Time: 2021-05-28T15:08:20.314+0000

• Duration: 87 min 32 sec

• Commit: a969084

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Test	Results
Failed	0
Passed	6860
Skipped	24
Total	6884

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Test stats 🧪

Test	Results
Failed	0
Passed	6860
Skipped	24
Total	6884