refactor: Modify placeholder set for hosts during development

We changed it to "all" because that's the convention we follow.
When running ansible playbook you need to limit the hosts with -l
so that it doesn't run on all hosts.

Some background on why it was set to default in the first place,
`hosts: default` is used as a placeholder during development
to indicate where actual host groups will later be defined.
You can define specific host groups within the inventory
file with names that are more relevant to your infrastructure,
replacing the "default" placeholder.

ansible/cheaha.yml

 ---
 - name: Setup node for use as a virtual cheaha node
-  hosts: default
+  hosts: all
   become: true
   roles:
     - { name: 'cheaha.node', tags: 'cheaha.node' }