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

When a dockerfile and a Procfile are present, the default entrypoint
should be /bin/bash 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.