Fix unit tests

Author: hgreebe

cookbooks/aws-parallelcluster-platform/recipes/install/cookbook_virtualenv.rb

@@ -49,6 +49,6 @@
     # tar xzf cookbook-dependencies.tgz
     # cd dependencies
     # #{virtualenv_path}/bin/pip install * -f ./ --no-index
-    #{virtualenv_path}/bin/pip install -r requirements.txt
+    #{virtualenv_path}/bin/pip install -r #{cookbook_virtualenv_path}/requirements.txt
     REQ
 end