Fix docker_id variation when using custom docker registry

[Grifs]

Describe your changes

Correctly use the custom docker registry settings when building a test script.
Add tests that check build and test steps

Related issue(s)

#678

Type of Change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New functionality (non-breaking change which adds functionality)
• Major change (non-breaking change which modifies existing functionality)
• Minor change (non-breaking change which does not modify existing functionality)
• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

Checklist

Requirements:

• I have read the CONTRIBUTING doc.
• I have performed a self-review of my code by checking the "Changed Files" tab.
• My code follows the code style of this project.

Tests:

• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

Documentation:

• Proposed changes are described in the CHANGELOG.md.
• I have updated the documentation accordingly.

Test Environment

[rcannood]

Minor suggestion