Use ansible_facts instead of the global 'ansible' namespace for system facts

[geerlingguy]

Right now there are a few instances in the book where I'm using facts like ansible_os_family and ansible_distribution.

Instead, I should start using ansible_facts, like ansible_facts.distribution (or ansible_facts['distribution']), as users could have INJECT_FACTS_AS_VARS set to false, and if so, none of the examples using specific namespaced magic vars will work.

This change was introduced in Ansible 2.5 (I think), therefore it has been present for a few years and will not cause any backwards compatibility issues with any supported Ansible release.

See related:

• Use namespaced ansible_facts ansible-role-repo-epel#44
• Add undocumented configuration parameter and explain in porting guide ansible/ansible#36059