[Isolated] Test python pacakges are installed when in an ADC region

Author: hgreebe

cookbooks/aws-parallelcluster-platform/spec/unit/recipes/cookbook_virtualenv_spec.rb

@@ -11,6 +11,7 @@
       context "when cookbook virtualenv not installed yet" do
         cached(:chef_run) do
           runner = runner(platform: platform, version: version) do |node|
+            allow_any_instance_of(Object).to receive(:aws_region).and_return(aws_region)
             node.override['cluster']['system_pyenv_root'] = system_pyenv_root
             node.override['cluster']['python-version'] = python_version
             node.override['cluster']['region'] = aws_region