[tests] Fix threading issue with parallel testing with non-threadsafe rspec mocks

Author: chadlwilson

src/spec/ruby/rack/application_spec.rb

@@ -794,6 +794,7 @@ def createRackServletWrapper(runtime, rackup, filename)
   end
 
   it "initializes initial runtimes in paralel (with wait set to false)" do
+    @factory = double("factory (non-tracking)").as_null_object
     allow(@factory).to receive(:init)
     allow(@factory).to receive(:newApplication) do
       app = double "app"