Fix #1564: Use Procfile for process types in Dockerfile apps

* Document new Procfile feature
* Add and update tests
* Fix a typo in generate_scale_file (ref #1923)

tests/apps/dockerfile-procfile/Dockerfile

@@ -0,0 +1,16 @@
+FROM ubuntu:trusty
+ENV LC_ALL C
+ENV DEBIAN_FRONTEND noninteractive
+ENV DEBCONF_NONINTERACTIVE_SEEN true
+EXPOSE 3001/udp
+EXPOSE  3000/tcp
+EXPOSE 3003
+
+RUN apt-get install -y software-properties-common && add-apt-repository ppa:chris-lea/node.js && apt-get update
+RUN apt-get install -y build-essential curl postgresql-client-9.3 nodejs git
+
+COPY . /app
+WORKDIR /app
+RUN npm install
+
+CMD npm start