Containers must not run as "root" user about deis

[gabrtv]

This is a bit trickier than changing the user on docker run. We'll need to make sure FS permissions are set correctly and ensure the UID always exists in the target container.

[gabrtv]

The idea here is to use the Config.user from docker image metadata in the case of Docker images. In the case of Heroku-style runtimes, we'll need to inject a UID into the buildstep image.

[gabrtv]

When users are specifying a Dockerfile they have control over the running UID (as well as UID/GIDs on the base image filesystem). We only need to solve the UID 0 issue for Heroku Buildpack style builds that use Buildstep.

[mboersma]

Now that Dockerfile build support is in Deis (containerize branch), this is simple: to run your app in a non-root container, put a USER statement in the Dockerfile.

Closing as "won't fix."