ADD step copies local node_modules to the container

[Guuz]

Hello,

On line 13 of the dockerfile (https://github.com/dockerfile/nodejs-runtime/blob/master/Dockerfile#L13) the local app files are added to the container. In the steps before the right node_module folder has been created.
But the step on line 13 will copy your (dirty) local node_modules over the (clean) container node_modules.
This is very bad for so many reasons! ;-)

ps. i'm using managed vm's with custom runtimes; a .dockerignore file does not work.

edit: I just noticed this is not the Google managed repo of the docker image. But this is probably still relevant. See GoogleCloudPlatform/nodejs-docker#22