Cherry-pick #22978 to 7.x: Fixed parsing of npipe URI

[michalpristas]

Cherry-pick of PR #22978 to 7.x branch. Original message:

What does this PR do?

Fixed parsing of http+npipe uris used by agent.

Why is it important?

Fixes: #22957
Blocking: #22394

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.

[elasticmachine]

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

[elasticmachine]

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Build stats

• Build Cause: Pull request #23014 opened

• Start Time: 2020-12-09T07:29:51.189+0000

• Duration: 69 min 47 sec

Test stats 🧪

Test	Results
Failed	0
Passed	16878
Skipped	1398
Total	18276

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Test stats 🧪

Test	Results
Failed	0
Passed	16878
Skipped	1398
Total	18276

[blakerouse]

Backport looks good.