Get output files when they have a suffix

[jsoriano]

What does this PR do?

Since elastic/beats#28927, Beats file output appends a suffix to all files, that can be also rotated.

This PR makes the following changes to address this issue:

• Tries to get files with the suffix if they don't exist without it.
• Configures rotation to try to avoid it.

Why is it important?

To fix autodiscover tests.

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 run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Follow up of Remove logging.files.suffix option and always use datetime suffixes beats#28927.

[mergify]

This pull request does not have a backport label. Could you fix it @jsoriano? 🙏
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.

[elasticmachine]

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Build stats

• Start Time: 2021-11-23T16:43:07.843+0000

• Duration: 41 min 5 sec

• Commit: 59b38cd

Test stats 🧪

Test	Results
Failed	0
Passed	248
Skipped	0
Total	248

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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[jsoriano]

Opening for review. If this continues giving problems, maybe it is better to setup Elasticsearch and use this output, as is already done for elastic-agent scenarios.

[ChrsMark]

Thanks for tuning the tests! lgtm if CI is happy :)!