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

Author: hgreebe

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

@@ -8,6 +8,11 @@
       cached(:virtualenv_path) { 'system_pyenv_root/versions/python_version/envs/cookbook_virtualenv' }
       cached(:aws_region) { 'us-iso-test' }
 
+      before do
+        allow_any_instance_of(String).to receive(:start_with?).with("us-iso").and_return(true)
+      end
+
+
       context "when cookbook virtualenv not installed yet" do
         cached(:chef_run) do
           runner = runner(platform: platform, version: version) do |node|