Use new venv for test role.

util/packer/jenkins_worker.json

@@ -59,7 +59,10 @@
   }, {
     "type": "shell",
     "inline": ["cd {{user `playbook_remote_dir`}}",
+      "rm -rf packer-venv",
+      "virtualenv packer-venv",
       ". packer-venv/bin/activate",
+      "pip install -q -r requirements.txt",
       "ansible-playbook run_role.yml -i inventory.ini -c local -e role=test_build_server -vvvv"]
   }]
 }