Execution by subgroups of subjects

[bclenet]

Changes proposed in this Pull Request:

• Run pipelines first levels by subgroups
• Apply this to pipeline testing as well

Checklist:

• Descriptive title
• Targets the main branch
• Changes are functional
• My code is explicit and comments were added to it
• Code conforms with PEP8
• Tests were added for the changes and they complete successfully
• Existing tests were updated (if needed) and they complete successfully
• Documentation was updated