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

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:

- https://github.com/geerlingguy/ansible-role-repo-epel/pull/44
- https://github.com/ansible/ansible/pull/36059

Search the book examples for ansible_os_family, ansible_distribution, and other globally injected fact names. Read each matching passage and update the examples to use the corresponding ansible_facts form, then verify that no affected examples still depend on globally injected facts.

Written by the indexing model from the issue text.