At least allow non root bootstrap - root bootstrap default but with override flag

[flybyray]

Proposed feature

Do not explicit require the decision made in commit https://github.com/robertdebock/ansible-role-bootstrap/commit/c7cc6d4eeff4c64584d76a5c1d9964e7b5395d15#r66724401

Rationale

Why is this feature required?

There are many ( if not most ) use cases where a real root user is unavailable ( deactivated or not allowed for remote access ).

[chris968]

Same problem for me, it break all my deployment.