Cherry-pick #23579 to 7.x: Fix flaky TestConfigurable* unit tests

[michalpristas]

Cherry-pick of PR #23579 to 7.x branch. Original message:

What does this PR do?

This PR adds a waitFor clause to TestConfigurableRun and TestConfigurableService tests.
Sometimes it happened that we were checking if process is not running anymore by checking state != Running but the process was (due to heavier load on the CI machine) still in the Configuring state. This condition then evaluated that process is not running and failed test.

Now we perform this check after we verify that status exited Configuring.

As i'm reenabling TestConfigurableService i will rekick tests multiple times and watch weekly failures mail.

Why is it important?

Flaky tests #20836

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/ingest-management (Team:Ingest Management)

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: Pull request #23591 opened

• • Start Time: 2021-01-20T15:42:35.120+0000

• Duration: 23 min 37 sec

• Commit: 4421fde

Test stats 🧪

Test	Results
Failed	0
Passed	1444
Skipped	4
Total	1448

💚 Flaky test report

Tests succeeded.

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Test stats 🧪

Test	Results
Failed	0
Passed	1444
Skipped	4
Total	1448

[blakerouse]

Backport looks good.