[IMPROVEMENT] Improve Asserts about terrible

[alegrey91]

Yes, the idea is to create a classic linter such as ansible-lint, yamlint and so on to facilitate the inventory implementation.
We actually cannot base our inventory validation on the ansible-lint because Terrible has actually a lot of built-in that cannot be recognized e/o understood by the linter.

[89luca89]

Current asserts works on ansible while using python3 version of it we should make it clearer

[89luca89]

Yes, the idea is to create a classic linter such as ansible-lint, yamlint and so on to facilitate the inventory implementation.
We actually cannot base our inventory validation on the ansible-lint because Terrible has actually a lot of built-in that cannot be recognized e/o understood by the linter.

This should be part of #94