CI: Add is_macos_controller Ansible variable for become_unpriv_available

This eliminates the need for ansible_facts to be gathered before
become_unpriv_available can be referenced.

tests/ansible/hosts/group_vars/all.yml

@@ -12,12 +12,12 @@ become_unpriv_available: >-
   {{-
     (
       not is_mitogen
-      and ansible_facts.distribution in ["MacOSX"]
+      and is_macos_controller
       and ansible_version.full is version("2.11", ">=", strict=True)
     )
     or (
       is_mitogen
-      and not ansible_facts.distribution in ["MacOSX"]
+      and not is_macos_controller
     )
     or (
       is_mitogen

tests/ansible/run_ansible_playbook.py

@@ -2,6 +2,7 @@
 # Wrap ansible-playbook, setting up some test of the test environment.
 import json
 import os
+import platform
 import sys
 
 GIT_BASEDIR = os.path.dirname(
@@ -36,6 +37,7 @@ os.environ['PATH'] = '%s%s%s' % (
 )
 
 extra = {
+    'is_macos_controller': platform.system() == 'Darwin',
     'is_mitogen': os.environ.get('ANSIBLE_STRATEGY', '').startswith('mitogen'),
     'git_basedir': GIT_BASEDIR,
 }