[DEVEXP-346] Allow docker type build from a repo with additional directory

This is the initial part of the work behind adding the additional directory to docker builds, especially this commit covers restructuring the `BuildInput` object splitting the docker related and STI related stuff into sub-objects. 
Still to do: 
- [x] docs
- [x] build image
Let's not assume Git only - we need to specify a type of repo probably (eventually pluggable).


> On Oct 10, 2014, at 1:22 PM, Andy Goldstein <notifications@github.com> wrote:
> 
> In images/builder/docker/docker-builder/build.sh:
> 
> >      exit 1
> >    fi
> >  fi
> >  
> > -docker build --rm -t $TAG $DOCKER_CONTEXT_URL
> > +BUILD_DIR=$(mktemp --directory --suffix=docker-build)
> > +git clone --recursive $SOURCE_URI $BUILD_DIR
> I don't think we should always assume the source will be git.
> 
> —
> Reply to this email directly or view it on GitHub.