Cherry-pick #20606 to 7.x: Fix yaml warnings in python scripts and tests

[jsoriano]

Cherry-pick of PR #20606 to 7.x branch. Original message:

What does this PR do?

Fix yaml warnings in python scripts and tests as proposed in https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load(input)-Deprecation

Why is it important?

To avoid using deprecated code that may stop working in the future.

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.

Related issues

• Related to Support Python 3.9 in developer tools #20384
• Part of Fix python deprecation warnings #20603

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

💚 Build Succeeded

Expand to view the summary

Build stats

• Build Cause: [Pull request #20661 opened]

• Start Time: 2020-08-18T13:17:59.017+0000

• Duration: 65 min 57 sec

Test stats 🧪

Test	Results
Failed	0
Passed	17987
Skipped	1853
Total	19840

Steps errors

Expand to view the steps failures

• Name: Install Go 1.14.7

  • Description: .ci/scripts/install-go.sh

  • Duration: 1 min 57 sec

  • Start Time: 2020-08-18T13:41:28.507+0000

  • log

• Name: Install docker-compose 1.21.0

  • Description: .ci/scripts/install-docker-compose.sh

  • Duration: 1 min 33 sec

  • Start Time: 2020-08-18T13:41:40.717+0000

  • log