fix(controller): dockerfile entrypoint should use /bin/sh

When a dockerfile and a Procfile are present, the default entrypoint for `deis run` operations should be /bin/sh instead of /runner/init, which is the default entrypoint for Procfile-based applications.

~~I've also changed the entrypoint for non-procfile applications to /bin/env. We've seen issues in the past with using bash subshells, specifically #2627.~~