tester: Update use of Node.js blueprint
tester: Update use of Node.js blueprint

The Node.js blueprint renamed cluster to containers;
this commit updates the use of that blueprint in the
integration-tester to use the new API.

kklin/kelda,kklin/kelda,ejj/quilt-dev,NetSys/quilt,kklin/kelda,LuiseV/quilt,kklin/quilt,LuiseV/quilt,kelda/kelda,kelda/kelda,ejj/quilt-dev,quilt/quilt,kklin/quilt,kklin/quilt,LuiseV/quilt,kklin/kelda,kelda/kelda,NetSys/quilt,NetSys/quilt,quilt/quilt,ejj/quilt-dev,kelda/kelda,quilt/quilt,NetSys/quilt,quilt/quilt,LuiseV/quilt,LuiseV/quilt,kklin/quilt,ejj/quilt-dev,NetSys/quilt